I mean, really, if one person keeps terrorizing the community, and the community is unwilling to defend themselves, then all the lessons about how rationalists are supposed to win have failed.

I agree, Rationalists should win! And in this case, winning doesn't mean turning into straw-man Vulcans who say "you shouldn't have any emotional reactions to people mass downvoting you" as I see a couple other places in this thread. Rather, it means that we should be able to design a community system that makes everyone feel cared for, and also provides them useful feedback for how they should or shouldn't post things.

Emotions matter, and making people feel valued and loved by other members is how a community thrives. (Thats why religions can do so well even though they make silly claims about the nature of reality).