Slashdot has (had? haven’t been there in a long time) a system in which you can upvote/downvote but also assign a reason, i.e. it’s funny, insightful, off-topic, spam. Perhaps it could be taken further so you could upvote a good comment but also signal you disagree with it somehow - this is especially helpful in political discussions as I don’t like to disrespect people I disagree with who are debating in good faith.