I was one of those who said they didn't approve of banning for content. I don't know how others would take that, but I was referring to conceptual content; I think regularly showing hostility or contempt could definitely merit banning, but that is not an issue of conceptual content. Even if someone makes comparative statements about demographic groups, e.g. "Irish drink more alcohol on average than Romanians" (not that I know if that's true or not), that does not necessarily show any contempt for anyone. That is more a question of attitude, although perhaps you could infer that someone has such an attitude if he makes obviously false statements of that kind on a frequent basis.
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?