They had no right to remove him from a seat that he paid for. If they couldn’t get volunteers they should have kept increasing the amount paid until someone finally bit. UNITED CREATED THIS PROBLEM BY OVERBOOKING THE FLIGHT, they’re the ones who should have to pay to get people to give up their reservations. Physical force should never have entered the situation at all.
Yup. That is exactly the point. The passenger had paid for the ticket and was even seated in the craft. If he didn't want to give up his seat, it shouldn't have had to. If it costs United $20k per seat, they'd have to make a cost/benefit analysis to see if it was worth it to the company to overbook flights. In any other industry, selling more tickets than you have seats available would be considered fraud.