I can tell you what the answer is on Hacker News, at least. You have to treat others respectfully here because if we allowed users not to, the community would decay, the best people (who incidentally have no trouble being respectful) would leave, and this place would become uninteresting, like scorched earth. That's the biggest risk to this site so we take it seriously.

I see this sort of argument a lot and I don't know how true it is.

Is it /really/ true that the best contributors are so sensitive? In my experience, these days it's actually the worst contributors or those who contribute not at all who are the most sensitive and liable to throw in the towel.

I'm sympathetic to your view but there is another risk that by overmoderating or catering to the most sensitive of contributors, HN will be left with non-interesting content, or controversial opinions will be silenced.

Why shouldn't we be (at least at first try to be) nice to people?

What possible reason? Is it excerting more effort? Does it in any concievable way affect the world in a negative way?

I'm sure your argument would be other people taking advantage, but being nice isn't the same as being naive. Give people the benefit of the doubt and the world is a better place.

Thankfully most nations laws and most private companies ToS extend beyond just physical harassment. He breached Twitter's ToS multiple times. Now he's banned.

You don't have to be nice to people, or show empathy, or refrain from saying hateful things; however, we are equally free to avoid associating with you.