So assume it's that your comment fell into the "noise" category and work harder on producing "signal" next time. We don't need to have a discussion every time someone felt that some post did not contribute sufficiently to the discussion.
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.