It would be a neat thing to test for DH1 and above comments. But do you really want to have to comment on "The author is a self-important dilettante" or "u r a fag!!!!!" However maybe I should be flagging these comments instead of downvoting them?
I get that not all downvotes NEED a comment categorically but there's some meat on the "downvotes deserve comments" bones.
Also: A couple times I have accidentally hit the down arrow. There is no undo. How does this relate to comment quality? The only remedy is to add a "Sorry, I downvoted you accidentally" comment, which I've seen people do. Although it's good etiquette that's a relatively low-quality comment.