Downvoting is a really bad idea, it destroys social bonds.

Just saying. "Punishing" bad content should be done on the social level like in the tight-knit human communities of earlier ages when people "behaved" because they didn't want to become pariahs in their communities. The threat of "not getting the community upvotes" anymore (because of bad behaviour) is much more effective and less damaging than outright downvoting