On individual comments and posts, the karma system is valuable for telling you if you're being stupid or not, and I appreciate it for that. The total karma score is (how long you've been on LW) * (how often you post) * (how much people like what you say); it says something like "how much you contribute to this site", which I find much less interesting, and I personally don't care if it's accurate.

I am, in fact, accusing people who downvote all posts by one person as using their time incorrectly; there are so many other things they could be doing that would make them happier and better-off, including nothing at all, that there's not much excuse for going through with it.

If my karma were reduced to zero, I would continue carrying on as I do now, commenting on this and that, and my karma would from then on be a positive number I don't pay attention to. A phlegmatic disposition has its advantages.