An idea I just had that might help civility is to require every post to "explain itself" with a limited set of tags. Sort of like the ./ point system in reverse; you would get some set of options like "Information," "Opinion," "Related," "Off-topic" and you pick one or more. So if you want to start making a fuss or interject something outside the immediate discussion, you have to announce it.

Doing this adds filtering metadata and an gives additional incentive to downvote comments that don't contribute - they're going to be more likely to use few tags or inappropriate ones. On the other hand, posts that use a lot of tags simultaneously and actually encompass all of them are probably detailed and well-considered.

Downsides: more work to post(not always a bad thing), more room for nasty rules lawyering("This is not Hacker News").