We as readers have seen it for decades actually. The moment a new writer comes on he decides to do something controversial and it makes readers either angry as hell or do a reaction of , hmmm that is interesting. Of course the fact is I could name many of the comics in the last 20 years like Identity Crisis or Green Lantern making Hal Jordan a Magnetoesque villain as we saw in the 90's. But that is so damn lazy and people constantly point to those and really , who wants to read the 100,000,000th billion rant on that ? I don't. So in this I wanna do controversy issues of books we have forgotten over time or the impact fizzled.
To start this I have been getting issues of Iron Man and well , I wanted to start off with him.
The Storyline - "Tony Stark goes insane and turns traitor."
What Happened - The story basically is this , Tony Stark has started to crack over killing a long time mentor an issue earlier. He had went to his Arctic bunker at the end of that issue (#318) of Len Kaminski's run . The death in that issue didn't seem to impact Tony Stark til the next issue in #319 by Terry Kavanagh .
In #319 , we see the 1st signs that all is not well in the life of Tony Stark. The death of his mentor has seemingly shaken him and he soon sees his dead parents . Which we think at 1st is a nice scene. But really the start of a chilling nervous breakdown for Tony. He runs into Happy Hogan and Pepper Potts who isn't that pleased with Tony which saddens him. He sleeps with Beth McCabe which we see him shed a tear over and then his dealings with Force Works has him take off when the Scarlet Witch confronts him over his handling the team and leadership. The scene at the end has her say "You used to be a good team mate Tony , what happened ?"
At the end we see a panel of a grimace of anger in his helmet to line up a meeting for all his friends at Avengers Mansion.
Of course this started the "CROSSING" storyline which tied into Kang influencing Tony Stark all those years and to handle it he became an alcoholic and womanizer . The idea was Tony was gonna always turn and go evil at some point for Kang. Finally the death of his mentor was the trigger event that sent Stark over the edge really. Where he would eventually turn against the Avengers and end up battling his younger teen self the Avengers brought from an alternate past...
The Reaction - Readers absolutely hated this storyline. Many claimed it was Marvel basically seeing what DC did with Hal Jordan and thinking , we can do it with Tony Stark. But unlike where DC put a whole new character in the mantle , Marvel stuck Tony Stark as a teenager there. Readers weren't kind and within issues Marvel realized the fuck up they had made. They used Onslaught and Heroes Reborn to fix this mess.
They would soon never mention Kang using Tony Stark to turn traitor either and it remains one of the forgotten controversial storylines Marvel ran before they revamped many of their stagnant books with Heroes Reborn.