Earlier quoted context omitted.
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…
I thought you meant literal bots. It can't be hard to figure out which accounts are downvoting and even rate-limit it per time period, per discussion, per user downvoted, etc.