Watts Martin distills the motivation behind GamerGate:
Those people form the core not only of GamerGate, but the larger culture war that bandies about terms like political correctness and social justice warrior.
When you learn to construct stories, you realize everyone is the hero of their own tale. No one sees themselves as the bad guy. Being confronted by someone saying this thing that you like is hurtful to others for reasons that you entirely missed is uncomfortable. We all know that racists and sexists are bad! If I like this thing that you say is sexist, aren’t you saying that I’m a sexist? Aren’t you saying I’m the bad guy? It’s all too easy to say no, you’re the bad guy, and to fashion a narrative that justifies going to war, literally or figuratively.