GG started because a guy wanted to say some people who claimed to be all about social justice and feminism are actually messed up and abusive. I'd say he's been pretty well validated over the last couple of years
I'd say it truly started when NeoGAF, SA, 4chan, and Reddit all mass censored discussion on the whole Zoe Quinn thing. THEN a bunch of publications put up the "Gamers are dead!" spiel all at one time, revealing that these people collude (which I think was confirmed as the mailing list or whatever was leaked).
I'm still convinced that had the discussion not been censored, people would have gotten bored of it and GamerGate would have never happened.
Comic books seem to be going through a similar thing right now, though it was more or less started when Marvel changed a bunch of characters to claim diversity points. It didn't help that the new characters were badly written, either. Then you have the writers of these comics shitting on their fans at every turn pissing even more people off...
I swear, California seems like a creepy fucking place.