Until there is skin in the game, those that go beyond down voting plagiarism and posts that fail to meet terms of service will continue to abuse their privilege. There should be a penalty to down vote something that doesn't warrant a down vote.

There's a large responsibility to having an account large enough to make significant damage to likely as many as half of the users at one time. Many of the mechanisms that led to down vote abuse have been curbed to a healthy level. Putting an onis on services that claim to be and are intended to prevent abuse that become abusive themselves would have an effect on abusive down voting.