As I've mentioned before, I 'moderate' another forum and it can be surprising how heated things can get. It hasn't happened for a while now, but we've had the cops call round at least four times over various threats, including a potential firebombing of a café, after the owner criticised some local healthcare activities...
I once had to stop two blokes organising a fight in a pub car park because one had made a joke about the fact that the other one had left the apostrophe out of the word "I'll" at the beginning of a sentence, making it look like "Ill" - the jokey way that he did this meant the the perpetrator of the missing apostrophe felt that he was saying that he made him sick...
We have people who find sport in causing issues - one chap is adept at posting ambiguous comments, then claiming that he meant the less obvious version, when challenged.
People sign up to start arguments, then sign up again to agree with themselves.
We have people immersed in conspiracy theories who consider that anybody who doesn't fully agree with their fantasies is being intentionally disrespectful.
Nobody ever censored that Hitler bloke on an internet forum, and look what he got up to...