I don't think the blame should fall on United though - they don't employ the security that used violence. Passenger doesn't listen to the flight attendants, police/security are called. And not listening to a flight attendant is a federal offense I believe.

I think you could compare this to a restaurant calling police to have someone who won't leave removed.. Police beat the guy up, restaurant isn't going to get blamed, police are. Really the same thing here. And the guy should take blame in causing the whole situation in the first place - doesn't excuse what happened to him, just that he had a role.