I feel like a lot of people who are interested in 'geeky' things like anime and manga and thus frequent this site are pretty young, so I like to give young people a pass for not being around in the 80s and only being very young kids in the 90s.
Let me tell you though that back then, something like race mattered about 1% of what it does now. Sure, it still mattered, in its own way, but it was normal and right to be "colorblind", as I still believe it is in the sense that it shouldn't matter what race a character is if that trait isn't part of the story.
There were of course, many less stories about gay people, although they were still there, and gender issues, well, no one ever thought about that stuff.
I think though a lot of young people alive today would be surprised to learn that there were dozens of hugely popular, mostly or all black TV shows throughout the 80s and 90s, and no one cared and no one made a big deal about it. They were mostly just shows about normal families doing normal things. There have also been strong female lead characters on TV and in movies and in books spanning all the way back, but sometime in the mid 2000s, people just seemed to forget all that, and rebooted the conversation from a premise that non white people, or leading women, or gay people had until that point, been broadly locked out of the media and story telling in general.
I think the problem now with so many stories about women or minorities is that the creators focus almost entirely on that one aspect, to a really, really cynical degree. It stopped being about good characters and stories, and started being about being a minority or a woman itself. For instance, the new Thor didn't just happen to be a woman, her being a woman WAS the point of the character, and not only that, she had to be an out and proud misogynist-punchin' feminist, complete with totally forced, painfully corny dialogue. I agree with what others have said. Marvel's audience doesn't hate diverse characters, they hate godawful characters, stories and blatant pandering and tokenism.
I've said it a hundred times already, but it bears saying again, 99% or readers or TV/movie watchers really don't care about the skin colour or sexuality of a character, but after a decade of this, they are getting really tired of stories and characters being used as cynical political mouthpieces. It's such a shame, because now we're at the point where it's just par for the course to have a wide range of token characters inserted into every story as if creators are required to fill in a diversity check list, and those that don't, even if they're wonderfully written, are attacked and lambasted by an outrage brigade quick to jump on anything that doesn't fit in with that current day's ever-shifting definition of 'diverse'.