I blame the marshals for what they did. United grossly mishandled this situation in many ways, but the one thing they did not do is beat a passenger.
I share your sentiment. United didn't harm the passenger, they just enforced their stupid bump rule, and when this arrogant passenger decided not to cooperate, they threw him off the plane. I am not justifying their act, but it's the police that is at fault, and somewhat the passenger. Always comply with law enforcement, don't be a smart***.