He had every right to remain ON the plane. He had purchased that right. United could not unilaterally remove that purchased right. A passenger can VOLUNTEER to give up that purchased right (usually for a larger sum that the purchase cost of the seat), but for United to forcefully remove a passenger after the passenger has fully paid their fare, is THEFT. United Airline’s actions in this case are more than reprehensible and they break their own contract with their passengers.