As I've said before, I think the best metaphor for a messageboard is that of a hosted party at someone's house. It's an open party: anyone can drop by. The host isn't really responsible for the behavior of his guests.
But in a way he is, because if enough guests behave badly, the other guests are likely to stop having fun. If a single guest gets too belligerent, she can ruin the fun for a whole lot of people. And the host, more than anyone else, is responsible for calming down (or kicking out!) the belligerent guest.
The host is also the one putting the most time into the party. Since he's the one creating it, it's really his choice what sort of atmosphere he wants. Some hosts like a rowdy atmosphere in which there's wrasslin on the front lawn; others like a calmer, quieter atmosphere. The guests may suggest a different atmosphere, but in the end, the host gets to decide what sort of party he's throwing.
Sure, flame wars can be allowed to continue. But that's not the atmosphere of this party. There's plenty of places online where flamewars may be carried out. The hosts here have decided against them.
Consider also that moderating isn't much fun: it means that you get to read the snarkiest, bitterest, meanest posts on the board, and you have to decide whether they're snarky, bitter, and/or mean enough to warrant action. The rest of you are free to ignore threads that have descended into ickiness. Not so the mods: they gotta wallow in it.
So although that ickiness doesn't bother you, keep in mind that it bothers the mods; and if we occasionally stop a conversation mid-ick when you think it could've continued successfully, it may be because (in addition to all Henry's excellent points) we don't particularly want to have to wade through another couple pages of ick before things resolve; and we don't want people getting lax about flaming, thinking that it's acceptable behavior. The more people that think it's okay to be snarky, insulting, etc., the more ick we've got to wade through.
Daniel