[META] Retributive downvoting: Why?

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?