Require sign-up. Implement karma, with voting. Restrict user commenting to 1/day until karma > X. No downvoting possible until karma > 2X. Put temporary blocks on users who derail threads or attempt to people-please with one-liners, etc. Ban users who attack other users.
Most importantly, make downvoting cost one karma point per downvote.
Most importantly, make downvoting cost one karma point per downvote.