I think this happens when a given ideal becomes an end in itself, and not a means to an end. Suddenly people's lives are based around this ideal, instead of the other way around, and anything that threatens this ideal seems to threaten their lives by extension.
I think this applies to evangelicals going after gays, movement atheists going after theists, and free software zealots going after anything and everything in the world that might make computing and coding more accessible to women. The way things are, or were, or should be, is perfect. If you don't exist in that ideal world, then you shouldn't exist at all.
I think this sort of inhumane idealism is worse than simple inhumaneness of convenience, because it actively seeks out people to destroy them, whether by conversion or by making life as something different impossible. And I think that part of the reason it gets so vicious about it is because it's sublimating the energy that should have gone into questioning its own assumptions, and hearing other people's stories.
I know in my case I spent most of my life not just willing to throw myself away for an ideal, but actively trying to do so. I spent years hating myself for not being the perfect Mormon, and struggling with Linux to try to get it to do what I needed it to. And when I found out that my theritype was a carnivore, I felt sick and wanted to cease to exist, because I felt like every day that I lived was a tragedy.
It's taken a lot of work to try to reconstruct my morality based on what's right for people, including myself, because of how much I saw the very idea mocked. It's supposedly weak, selfish, and dishonest to not sacrifice yourself. But the more I see how dishonest and selfish people who want others to cease to exist are, and how hard it is to convince myself that I shouldn't just curl up and die when I'm asked to, I start to question that. I guess.
I think this is why we're so quick to back down, to infosuicide even, and why it takes forever for us to get to the point where we voice our concerns about something that's hurting us. Deep down, we agree with everyone who's said we don't deserve to exist, for every reason. We consider every request made of us to be reasonable, by default, and every request we make to be an unreasonable imposition.
So when someone tells us to get the hell off their Internet, we already agree with them that we shouldn't be there.
It takes a lot of work to construct the illusion that we deserve to exist, and it's easy for that illusion to vanish.