I think it's hard to pinpoint a thing that just "started" it. The first use of the hashtag came from Adam Baldwin tweeting two videos about Quinn from Internet Aristocrat, the first of which was made around 10 days earlier. However it seems like it really blew up the following the "gamers are dead" articles which were released the next day.
The problem is with deciding whether the reason this story blew up was because of misogyny or because of dissatisfaction with the things that were detailed in the InternetAristocrat video. The video itself cover's the ZQ history, or at least a version of it. His complaints are about the DMCA against MundaneMatt, the gaming press jumping onto her initial story back in Dec 2013 about harassment from Wizardchan without looking further into it, the relationship with Grayson who gave her coverage in articles and the TFYC Reddit post among other things.
Now those are two guys who seem to be tied up with general anti-feminist/SJW stances so that is a bad start for the movement since clearly a lot of early supporters who were fans of these were going in with this mindset. However it was still tied to journalism ethics due to the fact that much of the ZQ outrage was tied to the perceived "sleeping with guys for good publicity" (which I'm not saying is true, just that that is a view I've seen quite a bit).
I do think a lot of it comes from a rising storm caused by friction between press and the gaming community though. It hasn't come to the forefront as much until now but for a long time a large portion of the gaming community have been unhappy with the press. I haven't been a part of it because I don't tend to frequent these sites anyway so it never bothered me but I have seen it. People have been mad about things like the closeness of the press (many perceived but unsubstantiated claims of bought reviews and journalists getting treated lavishly) and the industry and the increasing focus on op-eds that deal with hot topics like sexism. For sure there is sexism here too but I don't think that the Quinnspiracy and subsequent Gamergate could have happened in isolation. It seems almost inevitable, the Quinn part was just the spark that lit the swimming pool full of fireworks. It seems hard to say for certain that when this started, ethics had nothing to do with it.
Just for the record, I'm not an open GG supporter. I've never tweeted the hashtag and I find of the attention given by GG supporters to feminists and "social justice warriors" to be very off-putting, to say nothing of any death threats sent. So far I've just lurked around some GG havens like 8chan to see what people are saying. Most of the anti-GG stuff I've seen has just been snarky comments in unrelated threads on non-gaming sites or tweets (which are about the worst thing in all of this) so I just wanted to find a sane place to hear out the other side, but I do think there are problems here like early censorship on Reddit or the apparently tight clique of top indie devs that should be discussed and criticised, even if some people are using those for nefarious ends.