A few purported PIC here have stated it is their decision and an airplane is not a democracy and they call the shots.....
and a few purported PIC are quite wrong when discussing this particular, (or similar) situation(s), involving an airline, rather than a third level operator with 20seat aircraft at remote out stations. There are multi layers of airline traffic management, (ground staff), between the person who approached the doctor to ask him to leave and the most senior traffic services manager in the airline. At no stage do the lines of traffic management authority cross with those of the PIC when it comes down to a passenger seating dispute and the traffic staff would have valid grounds for complaint if a PIC tried to intervene. There would have been several more senior staff available that night who could have become involved, right up to and including the UAL Duty Station Manager, Chicago, if necessary.
To those posters using this thread to denigrate the pilot work force; PPRuNe is a professional pilots forum, please leave the chips on your shoulders at the door, before entering.
To those taking exception to the term Self Loading Freight (SLF); An understanding of aviation humour would probably be enough to stop you rushing into print.