I have an idea: Remove visible karma. Your personal karma is invisible to you and you have no feedback on how a post did. Karma is still used to kill comments, but everything above a certain score (say 5) is ranked arbitrarily (say MD5 of unix timestamp of comment).
Alternatively, make it public what everyone voted up on. That way everyone is open to criticism for what they voted on, and like people do on Facebook, they'll try to curate their upvotes so that they look sophisticated. Hopefully that will modify their upvoting behaviour.
Well, that's okay, isn't it? It's the idea that counts, so the discussion will still occur. It doesn't matter that it is centred around your comment that came after mine.
EDIT: Context for those who come after: Some other commenter said he downvoted my comment because he posted something similar. I assumed he said that to illustrate a flaw in my proposal and that he did not _actually_ downvote me. Since I can't find the comment that is similar (he's deleted what he's said), I'm leaving it up.
Alternatively, make it public what everyone voted up on. That way everyone is open to criticism for what they voted on, and like people do on Facebook, they'll try to curate their upvotes so that they look sophisticated. Hopefully that will modify their upvoting behaviour.