Why bother having a voting system at all, then? Karma that can only be seen on the user's page is simply just point-scoring. Sure, you gain minor functionality increases with karma, but you could do exactly the same thing with comment count for comments that aren't flagged (since you need to comment to get karma anyway)

Just give people a way to flag inappropriate comments, and then you've got pretty much the same system as we currently have. Early comments stay up the top, and there is no way to tell which has engaged the community apart from volume of response. Inappropriate comments get flagged and with enough flags they die. Get enough unflagged comments under your belt, and you're 'participating' and are then allowed the escalated priveleges.