If you make it possible for them to do damage on their home computers with no chance of being arrested and other people being visibly upset about it, a large number will opt to do so. [...] 4chan would have entire threads devoted to building worse hells. Yes. Seriously. They really would. And then they would instantiate those hells.

Wishing I could disagree with you, and, suspiciously, I find myself believeing that there would be enough vigilante justice to discourage hellmaking - after all, the trolls are doing it for the attention, and if that attention comes in the form of people posting your details and other people breaking into your house to steal your computer and/or murder you (for the greater good) then I doubt there will be many takers.

I just wish I could trust that doubt.*

*(Not expressing a wish for trust pills.)

EDIT: Animal experimentation and factory farming are still popular, but they have financial incentive ... and I vaguely recall that some trolls kicked a dog across a football field or something and were punished by Anonymous. That's where the analogy comes from, anyway, so I'd be interested if someone knows more.