I am thinking of the wider cases when people argue on this site, I admit.

If I start an argument with you, dear Rubi, and am deeply insulting, imo, anything you say either in retaliation or defense is mitigated by your right to defend yourself. We are not both equally guilty.

If someone is dumb enough to think they can bully someone else because they think they are a lot stronger, smarter etc, I think that there is some natural justice when they find out that the community will not tolerate their behaviour.

I can think of many instances where threads could be construed to be harassment.