Consensus seems to be that comments addressing downvoters, or complaining about downvotes, or asking for explanation of downvotes, are useless:
@Downvoter sends a notification to all downvoters for your post
Is it ever appropriate to question a downvote?
Can we have one-flag deletion of comments on SO (not Meta), like we have/had for accept rate comments, that contain the word "downvote" in some form? "@downvoter", "why downvotes?", "please explain downvote", etc.