The best form of moderation is not encouraging behavior that requires moderation. Downvotes are a form of community feedback but not really a moderation tool. For example, in cases where I am in doubt about the benefit of something to HN, my threshold for downvoting is much larger than my threshold for upvoting: I am more likely to upvote when "it might be useful" than to downvote a "might not be useful" because there is a person's karma at the other end of the arrow.
