It should be only fair that, when someone casts a downvote on MSE, the recipient of the downvote had a chance to respond. This is known at large as the right of reply or "the right to defend oneself against public criticism in the same venue where it was published".
I am well aware that this can't work on MSE for all downvotes, due to the outpour of low-quality questions and answers. Yet, it would be possible to add a new privilege to be awarded at some rep threshold, where any downvote to such a user's question/answer must be accompanied by a comment explaining the rationale. It could be as simple as adding a new popup to the downvote button where the casting user would be required to enter a comment.
I am not advocating for any particular threshold, be it 10k or 25k or 500k, but it would make sense to me that such a privilege existed. I am also not suggesting that the comment identified the originating user, just their reason to cast the downvote. Would be a plus if replying
@Downvoter notified them of any replies.