Oh, I beg your pardon -- I misread what you wrote as "... that thinks everyone posts ..." rather than "... that everyone thinks posts ...", and answered accordingly.
Having now (I hope) read the words you actually wrote, my intuition agrees with yours, but I suspect that it may only be artificial extreme cases that produce such counterintuitive outcomes. I will think about it some more.
I've gotten sufficient evidence from support that voiceofra has been doing retributive downvoting. I've banned them without prior notice because I'm not giving them more chances to downvote.
I'm thinking of something like not letting anyone give more than 5 downvotes/week for content which is more than a month old. The numbers and the time period are tentative-- this isn't my ideal rule. This is probably technically possible. However, my impression is that highly specific rules like that are an invitation to gaming the rules.
I would rather just make spiteful down-voting impossible (or maybe make it expensive) rather than trying to find out who's doing it. Admittedly, putting up barriers to downvoting for past comments doesn't solve the problem of people who down-vote everything, but at least people who downvote current material are easier to notice.
Any thoughts about technical solutions to excessive down-voting of past material?