Yes, I think many people are under the mistaken impression that the upvote/downvote buttons are functionally symmetrical, which is understandable given that the

Yes, I think many people are under the mistaken impression that the upvote/downvote buttons are functionally symmetrical, which is understandable given that they are presented as visually symmetrical. But upvoting serves to avoid redundant 'I agree.' posts, while if users downvote to disagree, it robs the discussion of valuable content (i.e., why they disagree). It would help if the UI were modified to signal this asymmetry.