In a Gordon Lightfoot AMA he notes the wreck itself wasn’t huge news at the time. It does appear in local newspapers as the ship had some reputation, and it did get a several page long article in newsweek which is the apparent source of Gordon’s inspiration, but it's fair to say a large part of the wrecks popularity worldwide is due to the song.

I can find no primary source that notes broad controversy about the song immediately after it's release, although I can find quite a few secondary sources claiming that. It would seem lots of people speculate on the family’s emotional condition. When you consider the kind of attention a pop culture hit like the song brings, it’s a double-edged sword.

Sue Hills, niece of wiper Gordon Maclellan notes

The song keeps the legend alive. It also tells the story. I have honestly hardly been able to listen to the song all the way through, though. Even 25 years later. Mr. Lightfoot really got to the heart of everything when he wrote that song.

Pam Johnson, daughter of Robert Rafferty, the ship’s cook (who has lines in the song) notes

I was really sad and mad when I saw people dancing to it, and when I talked to Gordon Lightfoot, he and I discussed if my father would say those words, and I said, "Yes!"

On one hand the song immortalizes the victims of the wreck and drives genuine public interest in the disaster. On the other, it can encourage exploitation of the disaster, and can prevent grieving in a proper way. While the feelings of the families are complex and varied, the wreck’s popularity as caused by the song would eventually lead to some conflict several decades later.

The wreck itself was located five days after the sinking via side scan sonar and a magnetometer. Lake Superior is a cold and relatively oligotrophic lake, meaning it doesn’t have a ton of biologically active nutrients dissolved in it. As a result, it preserves things quite well. There are a hundred or more shipwrecks dating from the mid 19th century to modern day mapped out in the lake, and they’re quite well studied. There’s a wonderful history of amateur divers in the early 70s performing dangerously deep dives on compressed air to map out some of these wrecks. At the time of Edmund Fitzgerald sinking, there’s already a brewing community of shipwreck historians and divers at the ready.

The wreck is 160 or so meters under water. This is probably beyond the limit for SCUBA on compressed air and it would be an incredibly cold, challenging and technical dive. The only thing that could reach the Edmund Fitzgerald were unmanned vehicles. The wreck remains mostly undisturbed and uninvestigated as a result. However, in 1977 another wreck in Lake Superior was re-discovered. The S.S. Kamloops, a somewhat notorious wreck that had sank 50 years prior was found by the same loose posse of recreational divers. Remember how Lake Superior is a lake low in biological activity? Well, that includes the bacteria and fish that would normally be decomposing the crew. The cold water is also perfect for the hydrolysis of fat, covering the corpses in a layer of waxy build up, further preventing decomposition. The Kamloops famously preserved the corpses aboard it. Ships like the Kamloops, and now the Fitzgerald are (like most shipwrecks for the record) also grave sites.

This brings up an interesting question for the historian and the amateur wreck diver: When is it okay to disturb the dead? There are legal, ethical, and social guidelines to follow. Doubly so when many of the dead’s loved ones are still alive and grieving. It's one thing to have a popular song written about your deceased. It's another to have their grave visited and disturbed by strangers.

With all that being said, when diving, it helps if your last name is Cousteau. Jean-Michel Cousteau (son of Jacques) happened to be filming in the St. Lawrence seaway, and happened to have a vehicle rated to 300m. Albert Falco and Colin Meunier took a 30 minute dive to the Fitzgerald as the first humans to lay eyes on the wreck. This didn’t cause much of a stir at the time, beyond the already sizable legend the ship had been developing. A further ROV expedition in 1989 filmed exterior shots of the wreck, got a Nat Geo broadcast out of it, but still, no notable public backlash.

Then in 1994 things get kind of wild (at least as far as freshwater shipwreck diving goes). There’s no less than three expeditions and the privately funded dives make some headway in exploring the wreck more thoroughly. This is my opinion, but I think this can be credited to the wreck’s mystique, driven mainly by the Gordon Lightfoot ballad. Of all the wrecks in the great lakes, I cannot find one given more attention. Frederick Shannon, a wealthy Michigan businessman was working on a book and documentary about the wreck. During his dive found the first recorded corpse on the wreck. Still clad in coveralls and a life preserver, the partially skeletal remains were visible out on the bow of the ship. It was the Kamloops all over again, except this isn't a relatively obscure steamer that sank in 1927.

Just to show that these interactions are more complicated than simple exploration, the same year divers at the behest of the families were able to bring up the bronze bell from the wreck, and it's been used as a memorial for the victims. Undoubtedly interest in the wreck enabled them to recover that bell, and allowed the families to have a meaningful symbol to memorialize a gravesite they can't reach themselves.

In 1995 something else happens. SCUBA technology at this point has advanced a lot since 1975 and that loose confederation of hobbyist wreck divers set their sights on what has now become quite a prize of a wreck. It's the legendary Edmund Fitzgerald after all. New gas mixtures allow for a very deep technical dive to the wreck itself. Two divers Mike Zlatopolsky and Terrence Tysall make the journey in a private expedition.

As technology improves the accessibility of the wreck, and its enduring myth ensures it remains an attractive dive site, it seemed inevitable to the families and loved ones of the sailors that the wreck would only get more popular. There are 29 sets of remains on that ship, quite possibly well-preserved in the cold waters of Superior. Zlatopolsky and Tysall recall getting calls from those families when word of their dive leaked. When Shannon revealed he had recorded photographs of corpses, they were incensed.

The families of the dead petition for restrictions on diving and are understandably upset at recreational and commercial expeditions to the grave site of their relatives. Activity on the wreck quiets for some time. Michigan passes a law in 1997 banning photography of any deceased in any human grave, shipwrecks included almost certainly as a direct result of Shannon. The pressure continues to mount from both the families and historical societies as Ontario waffles on this for some time trying to adequately protect the wreck and by 2006 it is firmly illegal to dive anywhere near the Fitzgerald without an archeological license or risk 1 million dollar fine.

This kind of intersection where the popularity of a historical site both threatens it but also drives interest in its historical reality isn’t uncommon. There are hundreds of wrecks in the great lakes alone and hundreds of thousands the world over. We understand what we do about this particular one, the Edmund Fitzgerald, largely because of its pop culture popularity. After all, it’s why this question is asked.

I can’t speak to the families but I doubt they needed Gordon Lightfoot, as sonorous as he is, to tell them about their tragedy. We do however, and so long as we don’t quite literally grave rob in our desire to know all there is to know about what happened, I tend to view the interest in historical realities a net positive one.