"Resist complaining about being downmodded. It never does any good, and it makes boring reading."
Agreed in full.
However, downmodding without constructive criticism leaves the downmodded with no sense of what to improve in the next comment. A downmod could easily be due to underdeveloped point, style, or disagreement about an opinion. At least 2 of the 3 reasons can lead to better future comments.
No, a discussion would create noise, which would not be valuable for the HN community. A voluntary, anonymous, tip about what made the downvoted comment noise would be more than sufficient. To avoid it becoming a discussion, no reply would be allowed. (Just to throw a half-baked idea out.)
Downvotes could easily become learning exercises that boost the comment quality over time.
The noise category assumption is a fair one. "Work harder" is a vague recommendation. Are there more specific recommendations you could make?
Don't treat post writing as an exercise in upvotability optimization.
If your post is < 1, add a link to a page about downvoted comments.
That way, the person who was downvoted has an opportunity to read about some common reasons why a post was downvoted, read tips on making better comments, and has more time to emotionally process being downvoted.