To me, a downvote on a posted article suggests it doesn't belong where it was posted, or the article is itself bogus, something along those lines. But (again, in my opinion) comments are fair game for downvotes if you disagree, and I will also do so if I disagree vehemently. But if you don't want to actually add something to the discussion, no vote is really needed. Maybe you ultimately disagree with a post or comment, but it gave you something to think about? If so, the comment contributed positively to the discussion.