Why is this down voted? I hate it when people do that and offer no explanation. Totally useless input, even harmful. HN should force comment on down-vote.
One reason that guideline exists is that unfair downvotes frequently get canceled by users who come along, see the situation, and make a corrective upvote. Meanwhile complaints like this linger on in the thread, inaccurate and off-topic—they don't garbage-collect themselves. As an example, I noticed your other comment and upvoted it before I saw this comment here. Similarly, other users have upvoted the GP.
As with any stochastic process, there is a lot of error and spillage with downvotes. There's no way to perfect it; you have to ask whether the system is better off with it than without it. Forcing comments wouldn't help, and posting complaints certainly doesn't help.
Why not have a meta discussion like a Wikipedia Talk page so comments like these would have room and critique won't be shut down.
Yesterday (you can look in my comment history) I ran into a situation where the person doing the down-voting turned out to be basing it on their opinion not fact (after they finally stated their opinion on the matter, which contradicts peer-reviewed research on the topic, I realized why they were down voting: insufficient depth of understanding of the topic) and no one came after them to correct the situation...
Either have people explain why they down-voted or have a Talk page where people can discuss their reasons, complain, etc, behind the scene.
HN is a site for intellectual curiosity (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...) and a meta forum would be a step away from that. It would fill up with litigious bickering and nitpicking, and demands for bureaucratic administration—all things that intellectually curious discussion requires having the restraint to avoid.
Edit: and it's for similar reasons that we don't publish a moderation log.
My other comment on this thread followed others in congratulating the author. It specifically said "Bravo!" and guess what? It got down voted.
So the explanation may be that it is useless input but believe me it is not useless to the author to have people congratulate them for the fruit of their labor. It's a human desire to be recognized by others. How is it not a positive comment? Why down-vote something as benign and empathic as saying congratulations? So force a comment on each down-vote and things might get a little bit better because at least we'll know it's not just random acts of hostility and that the down-voter has a rational reason for it, at least in their mind.
