What makes you think that karma is meaningless? I find it meaningful.

Sometimes I read a troll-like post, and check out the user that wrote it. If they have 3000 karma, it is likely that I am missing their point, and need to think some more. If they have -10 karma, then they are probably just a troll.

I know it's "bad" to judge someone by a number... but we do it because it is usually helpful.