I wonder what the userDB says about any scarcity of upvoters? Are there many others like me? Am I not pulling my weight? Should I do it more?
0: in particular, on HN the downvote button also seems to serve the purpose of "I don't think other people should see what you have to say" button due to HN's passive-aggressive greying out of downvoted comments.
Requiring a comment is probably a bit much, but I do think two separate downvote buttons would be helpful to the commenter, even if only they could see this feedback. Maybe one link labeled with "disagree" and one with "low quality" or something. UI-wise this would have the added benefit of letting new users know that HN officially expects them to consider both options.