I suppose the more correct term is that there was nothing stopping someone from writing a story were a character was right- wing and heroic or left-wing and villainous. Marvel was always left-leaning but they had not been gung-ho about Communism, portraying right-wing characters as Nazis or anything like that. The X-men are inherently left-wing but drew the line on extremism. Now, they ally with the worst mutants. Captain America is an inherently right-wing character but was nice with everyone and represented everything good about America. Now, he either heils Hydra or supports exclusively the left.
Look, I do not argue that they were absolutely even handed but things were better. Remember what MJ said? "Republicans buy shoes too." What does that mean? It means that he is a Democrat but in the name of making money, he will keep his mouth shut about politics. Marvel was willing to do that once too. They did not speak unless they were sure whatever they said would be something that all could agree on. Now, they side with the fringest of the left pretty much exclusively.