He's expressing his feelings. Doesn't he have a right to do that? I don't think anything constructive comes from censoring someone for saying that they are hurt or upset. I actually think it is very wrong and it makes me angry. But I won't down vote you in return, because you have a right to your opinions and I, as a matter of policy, do not downvote people for disagreeing with me.
If we can't express our feelings in safety what sort of community do we have? Voting may be a game, but it is a game that sometimes hurts people, especially when they have asked questions in good faith. Browsing through the archives for the many years of this site, I've seen post after post where people have written about real pain that comes from down votes.
If the down-voting action really had no meaning at all, why do it? If it does have a meaning, then I think we need to take care and consider what social signals we are sending.
I'm not saying we shouldn't downvote because it might hurt someone. Sometimes, down voting, even mass downvoting, enforces a very important and constructive social norm, e.g. don't plagiarize, don't puff up your CPAN module by self-reviewing it. The pain is the necessary if sad price for those important social norms.
Personally, I think by downvoting him for complaining you are enforcing a destructive social norm: "shut up, don't have feelings, don't react". A person who is told that message often enough will just walk away and leave. Is that what you want?
We want people to react to downvotes, at least to the right kinds. Otherwise they have no value for shaping behavior.
Expressing a thought or an opinion is fine. Desirable even, but when you post in the Monastery, you should be prepared to get answers from people that agree, and from people that (violently) disagree.
I tend to up-vote posts that
Add to the discussion (in the widest range, both technical and social)
Make me think
Make me want to post a reply (even if I eventually don't because the answer I wanted to post was already given or my answer would be inappropriate)
I tend to down-vote posts that
Add nothing whatsoever to a discussion
Reply with no useful info to threads older than 6 months
Are just complaints (and do not make me think or laugh like posts to hates-software)
I never down-vote Anonymous Monk. It's useless. I sometimes up-vote Anonymous Monk if the answer is extremely to-the-point and correct. I rather use my votes for named monks, but I think Anonymous Monk should stay!