There's a thread in the flight deck forum "rumors and news" on this incident:
United Airlines: Passenger forcibly removed from flight - BBC News in which a passenger was forcibly removed for "failing to volunteer" to leave an overbooked plane. Chosen at random, he was a doctor who needed to get home to see his patients. Excessive force was used so that the passenger had blood running down his face. Even worse, the passengers were being asked to leave to accommodate airline staff! Some posters on rumors and news think the airline behavior is Ok and that it's the passenger's fault. As a passenger I know that airlines exist to serve their paying customers. I've flown over 0.5 million miles with United, but never again. What do passengers, on this forum, think about this?