Have you considered adding a down vote button like Reddit has? I know you can flag comments above a certain karma level but I think that either giving everyone the option to down vote or having a lower karma threshold to down vote would allow the community to regulate itself.
Just a thought, but it seems to have worked for Reddit. This puts a lot of responsibility on the community to keep the quality of the discussions up, but I think enough people on here care about the quality of the community to help out.
