Also perhaps if a comment was controversial (i.e. lots of up and down votes), a list of the first users who upvoted it could be added next to the comment, e.g. "userA, userB, userC and 27 others upvoted this". That way, a stupid comment would be like the plague, nobody would want to be one of the first to upvote it (and therefore put their name next to it), and so it would quickly sink.