downvoting for disagreement. people on reddit treat upvotes/downvotes as agree/disagree, when they really should be used to promote thoughtful and good content, not necessarily what you agree with. If you think someone is participating in a thread properly, and promoting and inviting discussion and making the place better (even if you disagree with them) you should upvote instead.
reddit all too often let "lazy" comments float to the top because they were agreeable with the masses, but low effort.