How would you objectively identify such a thing? 'I think this downvote is dumb' isn't sufficient, obviously.

If the moderators have a record of who's doing the voting, it might even be possible for some form of AI to detect the most habitual negative sources.

It could happen.

For about the last year, about the only time I log in is to upvote somebody, and usually a while after I read their message. It can bug me for some time when it's one where I just can't settle for them being downvoted, or alternatively some upvotes are never enough.

Once logged in the sky can be the limit on my own comments sometimes, as I've mentioned before I guess all I have ever done is now known as responding to prompts.