What does rights have to do with anything? They had a reason to say "sorry for your luck and you have to now go." The reason doesn't even have to be a good one. If he's upset over that, he can 1) leave as instructed and later 2) address the issue. From that, the airline might make things right for him and possibly make some procedural adjustments so it doesn't effect others in this upsetting way. Another scenario is that if he's upset over it, he can (like before) 1) leave as instructed and later 2) address the issue, and if from that, he's not happy, then he can find more creative law biding methods to pursue. He could perhaps notify groups sympathetic to his situation and possibly garner media attention. If you want (more) sympathetic listeners, don't raise them to give reasons for us to blame the 'victim'.
Are you serious. Rights have a LOT to do with it. Suppose I walk into your home while you are relaxing on the couch and insist that you leave because I need your home right now. If you don't leave you should know that I have friends in the police force who will be removing you from your home. If you are upset about that you can leave as instructed and address the issue later.
Does that make sense to you as a reasonable response? Is that what you recommend we do? I don't think so.
If you are in your home, you have a right to stay in your home regardless of what someone else demands. It doesn't matter if that person owned the home before you and will own the home after you, if you are in your home you don't vacate based on the whims of any random passerby.
Why is this analogy appropriate? Because the Dr. in question purchased a seat on that flight for the duration of the flight acknowledging that it would be valid so long as the flying could be accomplished safely. That was HIS seat. Just like that is YOUR home. United was tresspassing on his seat and they should have vacated the vicinity of his seat as soon as he made it clear that nobody else was welcome to use HIS seat.
What kind of pansy pushover children are YOU raising?