Sorry WhitneyLand. In case you haven't noticed, the one thing Hacker News is most afraid of is becoming anything like Reddit.
We're not particularly interested in average jokes.
W/ respect to your specific "sad" example, the topmost comment on that thread gives the relevant information and has not been downvoted (as I'm reading it). The downvoted comment below it doesn't seem to add anything useful (but I didn't downvote it).
Plus, if you think something's been downvoted inappropriately, vote it up. People make mistakes sometimes.
It's not about being afraid, it's about not lowering the signal/noise ratio any further.
You should post a comment when, and only when, you have something substantive to say. There are many more downvotes than there are substantive things to say, which is why subthreads about downvotes invariably degenerate.
idea: you can track an explanation why something was downvoted without showing it as a comment. It can be shown only if a user clicks on some type of "why this was downvoted" link.
This would not lower the signal/noise ratio on the main thread. People can continue having a discussion that degenerates to low signal/ratio about the downvoting into this other link. If anything positive comes out of it, and enough people upvote it out of the downvoted status, then you can start commenting on it again.
This would also be aligned with the policy of posting a comment when, and only when, you have something substantive to say.
Because unless the comment was restored back to a positive score, you wouldn't be able to post a comment on the main thread (as a reply to that comment; not the whole thread). The policy would be enforced, and you dang wouldn't have to be telling people to not comment about downvoting.