But "downvote for disagreement" is a legitimate use. I personally tried to tell someone that it wasn't, and I got corrected by dang.
This made me realize it's a waste of one's time to write thoughtful, informative, educational posts only to have them buried and downvoted by man-children.
If we go by empirical evidence alone, it's a more effective use of time making Reddit-quality quips.
And, there have been times when I have upvoted something I disagreed with, because it made me think.
As an example, my point that it is fine to downvote for disagreement got a few downvotes. Ironic, no?