I'm a very light upvoter, but I'm pretty sure I have. I have certainly downvoted comments I agreed with. And for me, at least, karma simply is not "a popularity

I'm a very light upvoter, but I'm pretty sure I have. I have certainly downvoted comments I agreed with. And for me, at least, karma simply is not "a popularity contest only". (Incidentally, even if it were true -- which it isn't -- that no one ever upvotes a comment unless they agree with it, and that no one ever downvotes a comment unless they disagree with it, it would not follow that "karma is a popularity contest". For instance, that's consistent with the following state of affairs: people upvote comments that (1) are insightful and (2) they agree with, and they downvote comments that (1) are particularly stupid and (2) they disagree with. In that case, insightful comments will get lots of upvotes and no downvotes and stupid comments will get lots of downvotes and no upvotes -- unless it happens that someone posts something insightful and scarcely anyone agrees, or that someone posts something stupid and scarcely anyone disagrees. And if either of those happens, I submit that the community is so polarized that there's little hope of improvement with or without a karma system.)