On forums besides the Funhouse, I agree - abusive posts should be cut (or moved to the Funhouse).
On Funhouse threads... remember, the Funhouse doesn't go by *all* the same rules. I'm not against just pruning out the bad posts when they pop up instead of locking the thread - it just depends on the original thread. If it's something that's actually having a real discussion of some kind, then, yes, it should be pruned. Otherwise... 'meh.
But, I, personally, will consider this in the future. :D