Why do you care?

I am part of a community. Karma is a signaling process used in that community. I can participate, on many meta-levels, in the evolution of that signaling process. I am choosing to do so, because it is my wish that karma be an accurate signal for the worth of a particular line of discussion.

I.e.: to me, positive karma should mean that the post contributes to either the poster's or the the community's understanding of rationality; negative karma should mean that the post interferes with either the poster's or the community's understanding of rationality. A high karma post should mean "people should read this entire thread; it leads to a particularly useful realization", while a low karma post should mean "this entire mess is an appeal to various easily-stimulated cognitive biases".

When Karma is used to silence people because of things they said in an unrelated discussion, or social or political goals they have admitted to having, then karma is no longer serving the explicit meta-goal of lesswrong.com.

If I'm saying something terribly low-signal, downvote it. If I'm saying something particularly noteworthy or insightful, upvote it. But if I'm a guy that once got in a fight with you about human rights, don't downvote a philosophical discussion I'm having about identity five months later, if you actually care about the lesswrong.com community at all. Find some other way to destroy your enemies.