I am by no means an expert of any kind toward Norse mythology, but as I am very interested in Norse culture, specificly during the viking age (800s - 1000s), I hope my answer will steer you on the right path, at least until someone else expands on it. I'm not very well versed in Völuspá, but I have read "Snorra-Edda" (Prose Edda) and will use that as my primary source for this answer.

I don't believe anyone blamed Höðr for the murder of Baldur, but I would rather that the "Ásar" (Norse gods) would have blamed him for not seeing through the trickery. To try to give you an accurate response, I'll briefly cite what it says in the Gylfaginning chapter in the Prose Edda:

Baldur had several dreams about himself dying. As dreams were believed to often be forebodings of the future, Baldur began to fear his life. Since Baldur was very beloved by most gods and men alike, the Norse gods decided to do something about this fear. Frigg swoar on oath on Baldur ("put a spell on him") that he would be immune to all kinds of things, including metal and nature elements. It apparently worked so well for him that the gods held a gathering, and fooled around hitting him with various weapons that didn't do any damage to him. Meanwhile, Loki disguised himself as a woman and talked to Frigg about her "spell." She told him that she forgot to include a specific flower, and that the flower could indeed prove fatal. This story sounds awefully familiar to a Greek legend set more than a thousand years prior, but that's a story for another time. Anyway, Loki gathered this flower and headed back to the gathering. It is described as almost a circus, where almost every god is playfully inflicting what would be fatal wounds to Baldur. Left out of this is Höðr. Loki asks him why he doesn't join in. Höðr explains that he can't because he doesn't know where to aim, as he doesn't see him, and he doesn't have any weapons. Loki hands him the flower and tells him not to worry, as he will guide him. Höðr throws the flower that instantly penetrates Baldur, and he drops down on the floor dead.

Immediately after he dies the author says (translated by me): "And was that the worst accident to befall both men and gods." The word 'accident' implies that Höðr was indeed not to be blamed. Furthermore, the author says that the room was completely silent after Baldur died, and that everyone knew who did the deed (I'm not sure if the author means that they knew Loki was to blame, or Höðr, but I personally suspect the former). The gods first instinct was indeed to seek revenge, but since they were in their gathering place where they would host their parlament (old norse word "þing" used, as in the Icelandic "Alþing", although þing can also simply mean gathering), they couldn't seek revenge there as they were in a "safe haven." The sorrow was so deep among them that they couldn't speak, but immediately burst into tears. This is also an interesting passage as it wasn't deemed masculine to cry in old Norse culture, but that is also a topic for another time.

After Baldur's death, the gods first response was to send one of Odin's sons called Hermóður to retreive Baldur from Hel. Hel was a place very similar to "hell" as it was a realm the dead in Norse Mythology. Hermóður manages to get inside the palace of the dead at Hel, and finds his brother there in good shape. Hermóður speaks to Hel (the ruler of the realm named after her), and tells her that since Baldur was so beloved, he begs her to let him be free to leave the palace. She says that if he is really as beloved as he claims, she will release him if all things, both dead and alive, weep for his death. Hermóður goes back to Ásgarð (The city of the Ásar), and tells them the news. The gods send out envoys to ask that Baldur shal we wept out of Hel. Everything except an old lady cried for Baldur, and the author states that it is believed that the old woman was indeed Loki in disguise.

The significance of the story to me is not the fact that Baldur was killed by his brother, but the consequences it has. The gods are willing to go to great lengths in order to keep him alive, or bring him back from the dead. As I said, I'm not familiar with the older Völuspá, but in the Prose Edda, there is no meantion that I could find that the gods blamed Höðr for the killing of Baldur. The next chapter describes how Loki fled as the gods were so enraged by his acts for both his involvement in the killing of Baldur, and the prevention of his release from Hel. This is also a very significant story as this leads to the beginning of Ragnarök, through Loki's betrayal.

Now as to the moral issues of kinslaying during the height of the viking age. Since I am Icelandic, and familiar with the saga's, I'll use Iceland as a source for the morals here, as they may have varied throughout Scandinavia and other viking settlements. There are plenty of sagas of brothers being pinned against each other. This is usually because one is jelous of the other. Family was valued very greatly in these times however. The best evidence for that is the right of revenge. If a family member was murdered, that family had the legal right to revenge. Eye for an eye. So deeply rooted was this legal right, that it was inherited through five generations! Of course these matters tended to be settled during the parlament in the mid summer (Alþing), or other smaller legal gatherings during spring. The matter of killing someone as a revenge for someones death was therefore normal in Iceland during the first decades of its settlement. Revenge was often looked as a testement of ones honor. If a brother of a murdered man didn't seek revenge, he might be considered a coward by his contemporaries.

I highly doubt that people hearing these stories during that time would blame Höðr for the killing of Baldur, as Loki is clearly painted as the antagonist in the story. But as revenge was a normal thing back then, they might not have thought that the killing of Höðr was immoral. There is a great example in "Grettis saga" where his brother travels all the way to Constantinople to avenge Grettir's death. He kills the man responsible in cold blood in the middle of the busy streets in brought daylight. When the city guards run up to him, he doesn't even attempt to defend himself, but lowers his sword and explains that he was simply exercising his legal right. That was on the other hand not the law in the Byzantine Empire, and he didn't have any proof, so he was thrown into jail.

I hope this answers your question somewhat.

Additional reading: I found an English translation of the Prose Edda online. During a quick glance it seems to be fairly well translated: https://www.gutenberg.org/files/18947/18947-h/18947-h.htm#gylfe_XV

My sources: "Snorra Edda." Put together by Heimir Pálsson. 2003. Generally believed to be originally written by Snorri Sturluson at the beginning of the 13th century - This is a modern version of the old book, but I say it's highly reliable as it doesn't change anything except the spelling and grammar are in modern Icelandic. It still keeps the sentance structure and the wording of the historic text.

Other sources in this answer would be various Icleandic Sagas I've read in past years, and occational lectures I've attended that talk about them.

Take note that this is my first reply on this subreddit, so I may not meet all the standards perfectly to begin with.

Wow, you could not have made a question to catch my interest more perfectly if you tried. And so of course it was posted 10 minutes before I had to leave for work, forcing you to wait hours on end for an answer. Would have gotten this response up hours ago if I could have.

Anyways. For those who don't know the full story of the myth u/LegendarySwag is talking about:

Baldr was the most beautiful and well liked in the Norse pantheon. He began to have dreams that his life was in peril. Not wanting to lose such a gem as Baldr, the gods convene together and decide to request that Baldr be immune from danger. Thus, Frigg travels the universe and gets promises from everything that they will not harm Baldr. After these promises are secured, the gods make a game out of throwing things at him and watching them bounce off. Loki takes exception to this and decides he will find a loophole. He disguises himself and tricks Frigg into revealing that the only thing that she did not get a promise from was the mistletoe plant, for it was too young (which raises some interesting questions about perception of youth and knowledge). With this knowledge Loki goes and retrieves a stick of mistletoe. He gives the stick to Höðr, the only god not currently participating in shooting at Baldr (because Höðr is blind so does not know Baldr's location and he also lacks a weapon). Loki guides Höðr's hand and the mistletoe slays Baldr.

This is where the Prose Edda differs from its source a bit. The next bit has all of the gods too stricken by grief to even talk, but "no one could take vengeance, it was a place of such sanctuary" (Sturluson, 49). While Höðr is described as emerging from Hel with Baldr after Ragnarok, the Prose Edda actually does not specify how Höðr dies. In the Eddic poem "Voluspa" though we get this passage:

From that plant that seemed so lovely

came a dangerous, harmful dart, Hod began to shoot;

Baldr's brother was born very quickly;

Odin's son began fighting at one night old.

Nor did he ever wash his hands nor comb his hair,

until he brought Baldr's adversary to the funeral pyre (Poetic Edda, 8)

This quickly born brother, Odin's son who does not bathe until vengeance is taken, is Vali, not to be confused with the son of Loki that shares the same name. And to be explicitly clear, it is not stated in "Voluspa" that Loki is responsible for tricking Höðr, only what you see in the passage above. So Höðr is slain and Baldr is avenged and my summary of the myth (which I maybe used too much space on?) is done...but not really.

You see, Loki was recognized as the mastermind or the one at fault for this murder. The gods hunted him down and they punished him. And frankly, in my opinion, their punishment of him was much worse than simple death. They took Loki down into a cave with his two sons, Vali and Nar(f)i. Vali was turned into a wolf and tore Nar(f)i into pieces. They then tied Loki to three stones using Nar(f)i's entrails, which then turned to iron (in "Voluspa" only Vali is mentioned and it is his entrails that are used). Skaði came and put a snake above Loki's head, dripping poison onto him. Loki's wife Sigyn stands by his side with a bowl, catching the poison. When the bowl is full she has to step away to empty it, exposing Loki to the poison again. Loki remains there until his fetters break at the onset of Ragnarok. So the gods, and their Norse audience, did not leave Loki out of it. It was recognized that he had a major role to play and he was punished accordingly (possibly even egregiously).

But it is interesting that the Prose Edda leaves out the killing of Höðr (though, to be fair, "Voluspa" only hints at it). "Voluspa" is certainly the older work, with Snorri quoting from it several times throughout "Gylfaginning". So this could be indicative of a change in the perception of the act. Snorri was very Christian and his work does reflect that fact. I find it pretty likely that leaving out that act was an intentional choice on Snorri's part. Snorri does not shy away from expanding on the detail of actions throughout the rest of the Edda, so why skip over what would seem a somewhat integral part of the myth? As you say, the more modern and Christianized morality would have Höðr as an unwitting pawn and it would be wrong to punish him, at least to the degree that the older myth does. So perhaps this is Snorri making a small change to make it more palatable to his contemporary audience.

But that doesn't address what it tells us about "original" Norse beliefs. Is Höðr being killed a one off thing in the literature or is there a precedent that can be found? (I think you can probably guess the answer).

So before getting too far into this discussion though, I want to step back for a moment and explain an important factor in all of this. As with the other answer that got posted a bit ago, I'm focusing more or less solely on Iceland. A big part of this is that the majority of our sources for this sort of information come from there and it's what I'm familiar with. So really I shouldn't be using "Norse" in this answer because that implies that it would apply outside of Iceland. While this could be a safe assumption, it likely isn't. Iceland is a very unique entity and the rest of my answer is going to focus on an aspect of that uniqueness, namely feuds.

Now what do feuds have to do with the situation that Höðr found himself in? Well many feuds in the sagas are kicked off by someone murdering someone else. And there is always a need for compensation of some kind. In the sagas you get situations where, for want of better terms, the case gets taken to court. This involves the accused and the accusers having a mutually agreed upon arbitrator look into the matter at a þing or alþing and deciding on the proper course of action to make reparations. This aspect of the set-up doesn't really concern us though. What does concern us about feuds is vengeance and how kinship and responsibility play into it.

Now the example given by u/Liljendal from Grettis Saga is a pretty good one, with the brother traveling all the way across Europe to exact vengeance. It shows just how strong the idea of kinship was and how far some were willing to go to uphold honor. My personal favorite is in Gisla Saga. A short summary of which is:

Gisli murders his sister's husband in revenge for him having killed Gisli's other brother-in-law. The sister, Thordis, proceeds to marry her first husband's brother (Bork) and continuously goads him into hunting down Gisli. After 13 years, they finally catch Gisli and murder him. At the celebration, Thordis stabs one of the men in revenge for killing her brother and declares herself divorced from Bork. (Quoted from here)

The main thrust of Thordis goading Bork into hunting down Gisli is that if Bork allows Gisli to get away with his brother's murder, Bork is a coward and dishonored (Her point is helped by Gisli ignoring the decision of the arbitrator, namely that Gisli was outlawed and should have left Iceland). So there is a consistent thread of needing to maintain one's honor throughout Icelandic literature. When you or your kin have been wronged, you must attempt to resolve the matter, even if that ultimately means exacting vengeance.

Another aspect that shows up in Gisla Saga is the idea of "collective liability":

The target need not be the actual wrongdoer, nor, for that matter, need the vengeance-taker be the person most wronged. (Miller, 180)

In Gisla Saga, this shows up when Bork is not part of the group that catches and slays Gisli. He is sitting at home while the fight rages even though he has the strongest claim to vengeance. The other facet shows up as well, with the target not being the wrongdoer. The murder that sets off the main events of the saga is the murder of Vestein. Gisli has dreams that indicate the killer as being Thorgrim but Thorkel was the one who was (arguably) wronged (sorry, this saga is ridiculously complex but that's why I love it so). So Gisli slays Thorgrim. But again, this is based entirely on prophetic dreams. Later in the saga, Vestein's two sons feel that vengeance has not been meted out fully, and so they proceed to hunt down and kill Thorkel. So regardless of which of the two men killed Vestein, one of them was killed wrongfully.

So would the slaying of Höðr have been seen as immoral? Not likely. It would have been understood that it had to be done, even if it was regrettable. As the one who struck the killing blow he was at least partially responsible (which is more than can be said for some victims in the sagas) and had to pay and I still say that Loki paid much more. In addition, there is some evidence of a change in views on the matter as Snorri leaves out the killing of Höðr.

I know my answer does not differ overly much from the other here, but I hope that it sufficiently (and clearly) expanded on some of the details. If you have any other questions just let me know.

Sources

Byock, Jesse. Feud in the Icelandic Saga. Berkley: University of California Press, 1982.

Miller, William Ian. Bloodtaking and Peacemaking: Feud, Law, and Society in Saga Iceland. Chicago: University of Chicago Press, 1990.

Poetic Edda. Translated by Carrolyne Larrington. New York: Oxford University Press, 1996.

Sagas of the Icelanders. Penguing UK, 2005.

Sturluson, Snorri. Prose Edda. Translated by Anthony Faulkes. London: Everyman, 1987.

Unfortunately, you are likely to find the answer to this question deeply unsatisfying.

 

This particular story is transmitted via the Danish author Saxo Grammaticus and the Icelandic author Snorri Sturlusson, both writing in the latter half of the 12th century, and possibly with some sharing between the two authors and works. Saxo Grammaticus is generally thought to have been a clerk for the Archbishop of Lund. Sturlusson was a lawspeaker and chieftain who was nevertheless heavily involved in the Church politics of Iceland. Both authors endorsed the theory of euhemerism when it came to Norse mythology - the notion that the Norse pantheon were originally flesh and blood individuals who were reinvented as deities by successive generations of oral transmission and myth making. Indeed, Snorri contends with the Prose Edda that myth ought to be embellished, to keep the myths relevant.

 

In other words, we don't have any sources for how a Norse pagan would interpret this tale. In fact, we can't be certain that the version we have is as the Norse pagans would tell it, or that it isn't a complete fabrication. We also can't be certain that the tale was common to all of Norse paganism, rather than a specific locality like Iceland.

 

In a more general sense, the Norse did not approach justice and morality the same way that modern societies do. A feud could be settled privately; with payment of various sorts, a duel, or even small-scale warfare; or it could be appealed to a Thing, an assembly of all free men in a polity which had the capacity to impose fines, outlaw individuals, or just tally up all the deaths and wounds on each side, set them against each other, and order the remainder paid out. There's an interesting account of this in the Eyrbyggja saga:

 

Steinthor went home to Ere in the morning, and no more fighting there was thenceforth through the winter. But in the spring, whenas time wore on to the days of summoning, men of good will bethought them that things had got to a sad plight, inasmuch as those men were unappeased and at strife together, who were the greatest in the countryside. So the best men who were friends of either side so brought it about that it came to seeking for peace betwixt them. And Vermund the Slender was chief of these, and with him were many men of good will, such as were allied to one side or the other, and thereof it came afterwards that truce was settled and they were brought to peace, and most men tell that these cases fell under Vermund's dooming; but he gave forth the award at the Thorsness Thing, and had with him the wisest men who were come there.

Now it is told of the peace-making that the slayings of men and onslaughts on either side were set off one against the other. The wound of Thord Wall-eye at Swanfirth was set against the wound of Thorod, son of Snorri the Priest. Against the wound of Mar Hallwardson and the stroke that Steinthor fetched at Snorri the Priest, were set the slayings of three men who fell in Swanfirth. The manslaughters which Stir made in either band were equalled; but in Swordfirth the slaughter of Bergthor and the wounds of Thorbrand's sons were set one against the other. But the slaying of Freystein Rascal met the death of one of those unnamed above who fell in Swanfirth out of Steinthor's company. Thorleif Kimbi had atonement for his lost leg; but the man who died out of Snorri's company in Swanfirth was set against the onset wherewith Thorleif Kimbi had set the fight agoing there.

Then were the wounds of other men set against each other, and what was deemed to be left over was booted for duly, and so men parted from the Thing appeased.

And that peace was well holden while Steinthor and Snorri were both alive.

Source

 

They likely wouldn't have considered Höðr fully at fault, but that doesn't mean he couldn't be killed in retribution for his role. Scandinavian societies tended to draw distinction around slaying that was done openly, as in the case of Höðr, and that done secretly, as in the case of Loki; rather than intent.

 

Primary sources are obviously the Gesta Danorum, the Prose Edda and the Eyrbyggja saga. For secondary sources Song of the Vikings: Snorri and the Making of Norse Myths is relevant and fairly approachable.