Sadly the European subreddits are increasingly overrun by Nazi cretins and their quisling allies so this kind of opinion is really common in that section of reddit.

Several crusades didn't even target Muslims or Muslim occupied lands, namely all of the Northern crusades, the Albigensian crusade, the Bosnian crusade- these targeted European heathens and heretics- and the Fourth Crusade, which was supposed to have targeted Egypt, but instead ended with the sack of Constantinople, which ironically help bring about the downfall of the last strong Christian state in the Near East.

There was also the Rhineland massacre of thousands of French and German Jews (as well as the forced suicide and forced conversion of others)- although that is considered part of the People's Crusade targeting the Muslim Seljuk Turks.

Regarding the crusades that did take place on Muslim lands: similar questions have already been addressed in previous AskHistory threads, see here, here, here, here, here, and here. Several of these threads further link back to even older threads discussing the same topic. It's been a popular question here since the rise of the alt right.

Some of the threads I linked have really interesting and informative responses and I recommend reading all of them but the basic takeaway is:

1. There were many crusades fought for varying reasons, of which the religious justification was only one; it's inaccurate to boil all of the motivations behind each of them to "Christian retaliation against Islamic expansion."

2. The framing of the Muslim expansion and the Crusades as a Manichean struggle between Christianity and Islam has a lot more to do with current events (and the way certain ideologues try to spin them) than historical reality. Plenty of Christians (and Jews) participated in the "Muslim" conquests, for example.

EDIT: Thanks to /u/shlin28, /u/textandtrowel, /u/Epyr, /u/Ambarenya, and /u/thejukeboxhero for their excellent responses in the threads linked above.

"Why the crusades happened" is probably one of the longest running historical debates. If our mods would be so kind as to let me add my sources (Christopher Tyreman amongst others) when I get home, I'll give you my overview of the subject. Keep in mind, when I refer to Islamic expansion and Muslim conquests, I am referring to the geopolitical aspect of these events as well as religious.

To make note of what has been said by u/specterofsandersism: You can almost never boil historic events down to one cause, especially spanning as long a time as the whole crusading movement. However, it cannot really be denied that the Crusades as we understand and discuss them would not have been possible without some level of religious and/or cultural conflict.

First of all, "Crusade" is a retroactive word. It wasn't developed until after Europeans realized that there would be multiple armed pilgrimages or expeditions as the First Crusade was sometimes known. Second of all, the northern anti-pagan and anti-heretic crusades were only connected to Islam via the idea of a Crusade. So, let's limit the scope of this question to those Crusades that went south and east into Egypt, Anatolia, the Levant, Syria, and the Holy Land.

Were those Crusades intended to counter Islamic Expansion? Well, you can only use that reasoning for so long. Is an event 700 years after an event able to be considered a counter movement? I would argue not. I think its difficult to even say the first Crusade was a counter to Islamic Expansion. One one hand, that counter came 400+ years late. On the other, the apparent impetus for the First Crusade was apparently (supposedly?) the Byzantine Roman Emperor Alexios calling on Pope Urban II to send aid in reclaiming territory conquered in the Muslim conquests, and reclaiming Jerusalem was a centerpiece of Urban's call to arms. By that logic, the first Crusade clearly motivated, at least in part, by undoing the Muslim Conquest. Of course this brings you into the highly debated issue of whether or not that was their real and sincere motivation. There are some historians, usually with some kind of economic focus, who will argue that the Crusaders were actually trying to secure access to Middle Eastern trade and land wealth. Certainly, given the number of European nobles that became feudal rulers in the Outremer, this must hold some truth as well. As with most things I suspect it to be a combination of the two, as well as other contributing factors.

Moving beyond the First Crusade, I think the Second and Third Crusade have a claim to the idea of "countering Islamic expansion." The argument against this would probably be that Islam couldn't really expand back into the Outremer if it never really got expelled. However Islamic rule was expelled and did "expand" back into the region. This was, generally, the cause of the second and third Crusades in the form of the Seljuks and Ayyubids, respectively. The Second Crusade was essentially a call reinforcements to defend the Outremer from the Seljuks and the Third was a reprisal to Saladin's conquests. In both cases, I would consider it a response to Islamic expansion.

Even going into the Fourth Crusade, a spectacular failure though it was, you could make the argument that, like the First, it was a counter to Muslim reoccupation of and expansion into the Holy Land, though by then that case has somewhat waned. Any later than this, or in any other location, and it is definitely not a counter anything, but just a standard offensive.

In summary: the Crusades began, at least in part, as a counter response to the Islamic expansion, and were prompted by Islamic reoccupation of those same territories multiple times.

Sources:

Gibb, Hamilton. The Life of Saladin (Oxford: Oxford University Press).

Housley, Norman. Contesting the Crusades (Oxford: Blackwell Publishing. 2006).

Jerusalem the Golden: The Origins and Impact of the First Crusade. ed. Susan B. Edgington and Luis Garcia-Guijarro (Turnhout: Brepolis Pubilshers. 2014).

Kedar, B.Z. (ed.), The Horns of Hattin, (Hampshire, 1992).

MacEvitt, Christopher. The Crusades and the Christian World of the East (Philadelphia: University of Pennsylvania Press. 2008).

Tyreman, Christopher. The Crusades: A Very Short Introduction (Oxford: Oxford University Press. 2005).

Tyreman, Christopher. How To Plan A Crusade (UK: Penguin Books. 2015).

Edit: Sources