zlacker

Let moderators mark a comment as "not useful". And everyone who voted for that comment earns negative karma. This will make people think twice before voting for a comment. Dumb and mean comments won't be voted on.

This allows you and the mods to set the tone for comments.

Of course, the weak point is - moderators bias may show up. And a worthy comment may be marked as not useful occasionally. So depending on the number of moderators you have, you could make it so that the minimum criteria is x number of moderators have to mark a comment as not useful.