Some ideas

You'd be surprised how forgiving the community is, if you read this study. Someone can sockpuppet, edit war, canvass, and deceive so that they can push their viewpoint. But if they promise to be good guys, they can come back, repeatedly. Many people learn from their first block and become great guys. Many people learn from their second block too. But others just become smarter, and find ways to barely meet policy, and push a viewpoint. The rare time they cross the line, they've acquired enough supporters who are really just pushing the same viewpoint. You see a few barnstars, and all is forgiven. I wouldn't reward these editors with anything more than 20 characters.