I understand it wouldn't work in all cases and I guess I'm fine to remove them when it's descended into nothing but insults (like you can't even make a point to include with your insults!).
If you had a lines thread, and then it turned into what line abdelkader should play on, and then it turned into a discussion about only abdelkader and what he would bring to each line, and then it goes to just abdelkader stats and intangibles.....
Well at some point you could just split it into two threads. People who want to keep talking about abdelkader can do so in the new thread and people that want to talk about the rest of the lines can continue in the old thread.
EDIT: Maybe abdelkader example is something you might just let go. If it's some polarizing topic at the moment that keeps getting brought into discussions (like Cleary or Howard or Holland) that people are getting sick of, then split it up and remind people that they don't have to go into the new thread if they don't want to discuss the topic
I'd vote for the split thread idea. If some conversation evolves into something else and you really, really don't want it to continue in that thread, then why not just grab all the posts and stick them in a new thread (or an appropriate existing thread) with a link to said thread?