I am not interested in whether it was or was not legitimate for United to remove the guy from the plane, because by the time security got there to remove him, clearly authority was on their side. The doctor, David Dao, undoubtedly did not know the legal ins and outs of whether it was reasonable. His whole justification seems to have been: I am doctor, therefore I am important. I am more important that anyone else you could remove from this plane, therefore I am not leaving. This is the kind of "individual exceptionalism" that I see people use all the time to break rules. In general, we might want to favour doctors in this sort of situation, but he was in no position to determine that. It's not as though he had an emergency that he absolutely had to deal with; no, he just had patients to see the next day. At that point, it's not up to him to decide if his reason for going is more important than another passengers. Sure, he has the right to complain; he has the right even to sue the airline if the situation is egregious. But he is not in a position to tell the airline that he is not going to get off, period.
The thing that puzzles me about this is what he hoped to gain from it. Prior to the arrival of security, I imagine he hoped that protesting loudly enough would get the airline to move to an easier target. I'm sure the airline would have liked to, but letting one person insist on staying aboard is certainly not fair and is likely to backfire when they have to explain to the next person in line that he, and not the doctor, has to get up and leave.
But after security arrived, what then? According to what I heard on the radio today, security informed him that he needed to come along, and he said that they would have to drag him. It's kind of hard to imagine any other scenario playing out. They don't want to drag the guy; it's a hassle, whatever else it is, and their lives would be easier if he walked off. So it wasn't like they just came up and pulled him out of his seat. He refused repeated requests to get up peacefully, and he knew that the consequence was that they were going to take him by force. Had he just lost his mind at this point? Is he thinking that he will show up United by forcing security to take him away aggressively? Is he thinking ahead to a lawsuit? (Also on the radio, I heard that he said something about suing United before they pulled him off.)
I have a hard time imagining myself reacting the same way. No matter how angry I might be, I would be thinking of what actions I would take after I got off the plane peacefully. I really can't see asking to be dragged off the plane. Perhaps if I had a true emergency, like one sees in t.v. shows -- "I have to get to that hospital tonight or a man will die! I am the only person in the country who knows how to perform this operation!" -- I would have resisted. Otherwise, no. Again, whether it was fair or not for this man to get bumped is no longer the question once security arrives. Someone with more authority than him has decided that he needs to get off the plane. He is going to get off the plane one way or another. Why choose the painful and embarrassing way?
As a final note, I wonder what the protocol is for removing passengers. Surely security has some kind of standard way of doing this if a passenger resists. They may never use that in their lives, and maybe they didn't remember at the time, but why even have security if you're not going to train them how to do the job? The reason I ask is that dragging a person seems like one of the worst possible ways. Heaving him over one's shoulder would seem much easier. With three security guards there, they could surely have gotten him up and onto the back of one of them, and the other two could have helped support the weight. It was probably very tight in the plane aisle, which is the best reason I can think of for not using this method. But if you've ever tried to drag someone, you know how difficult it is. They seem to have chosen the method most difficult for themselves as well as most embarrassing to the passenger. But maybe this is what they're supposed to do; I'm just curious.