So. Good.
This is kind of somewhat true.
Although there are many mature individuals in the FGC there are many more who aren't.
There's shit tons subtle racism, sexism (streams going out of control when a girl pops up, referring to some members as "traps" "faggots" etc)
Honzo is right in the fact that it is not primarily a FGC thing (I so bet it happens in LOL or SC circles), but it should not be tolerated just because it isn't
Stream chat is something totally separate from the actual fighting game community though. Streamers do what they can to regulate, like by putting up sub-chat or banning people. When 13k are in the chat, they really can't catch anything but massive ascii or juri fanfic though and mods are there to watch as well, not to just sit there with their eyes on the chat the whole time.
The claims like the twitch guys and all the non-fgc people make about the scene are just irritating though. They talk about all this racism and sexism going down, then I say "what do you mean" and then they're like "oh, circling the wagons again, eh sexist racist guy?" It's impossible. If they know specific players doing this crap, bring it up specifically instead of throwing everyone under the bus.
The one thing I can think of since Cross Assault is ChrisG's tweet to mrwizard calling him a "faggot" and that did not go over well. Most people got the picture that he's a terrible sport and abrasive as hell. People only seem to heckle him harder after that, but what else can anyone really do? Is he supposed to be banned from tournaments now? That would open some ridiculous cans of worms. They tried the yellow card stuff a long time ago. It was just silly because it's not nearly as cohesive of a scene as people think. It's still very much just large individual gatherings of fans of fighting games.
You're damn right it happens in SC and LoL and every gaming scene. I'd wager they're worse. The pro players in those scenes are bound by contracts to not blurt out anything. Think about that--most of our guys are not. But I don't know anything specific, so that's just my paranoid speculation