The assumption that bad comments will get less votes is a canard. As the community grows, the same people adding comments also add their votes. If anything, they're more likely to vote since it's just a click, and so noob votes will drown old users even more. It's not just downvotes but any votes that have negative social consequences.
Update
[1] Exhibit A: http://news.ycombinator.com/item?id=1021157