Technical workaround:
Make it so that you cannot upvote/downvote from a user's comment history page. Or rather, show the vote as counting to the person pressing it but don't actually tally it.
EDIT: Ok, I see that the buttons have been taken off so this is irrelevant. In that case, new proposal: put the buttons back but make them do nothing. The majority of LW won't read this post and I think you'll be able to fool those who go to mass-downvote comment histories.
I kind of like your second plan.
Several people posted recently in a thread on women, mostly espousing feminist views - only to find that someone had declined to respond to their post, but instead browsed their history and downvoted every single comment or article they had ever posted.
I have two questions:
1. Why would you come to a site like this and pollute the karma system? How does it make you smarter? How does it make anyone else on the site smarter?
2. What would be a good technical workaround? In my mind, some system that detects mass-downvoting and flags a user for review would be preferable, but what should happen then? Should the system be more lenient to higher-karma posters? Who should perform the review process? What should be done with those whom the reviewer ascertains are abusing the karma system? I would prefer some kind of lesson that is more corrective than retributive - it seems to me that people who would perform this behavior are exactly the sort of people who need some of the lessons that this site provides. Any ideas?