I don't want to state the obvious....but
The mods (here, ch4, other forums) constantly tell posters not to retaliate. Just report it and move on. Hardly anyone does that. If someone makes nasty comments report it then go to another thread or post round it. Don't even acknowledge it.
How many times do we see threads with personal attacks, nasty comments and then everyone piles in posting smileys, making jokes etc? Yeah it lightens the mood but it also keeps the thread at the top of the forum and draws attention to it. That's not just in HM dispute threads btw.
People read the whole thread then post to say how bad some comments/people are. Again drawing attention to it and keeping it going
Nothing will ever change if people keep acknowledging the troublemakers