I dont like the idea because people will start modding others down based on personal opinion. People will be in fear of getting modded down if they attempt to step out and express their real feelings about a matter.
I agree that that's a possibility, but I think that the majority of people around here want to have good conversations.
Also, /. implements meta-moderation so that the moderation can be rated.
That might be a bit much, but at least starting out with some kind of ratings system might be good - again, based on someone's posting history.