If I feel that my seat on that flight is worth more to me than what the carrier is offering, that is MY DECISION, not the carriers.
That being said, I don't understand why they needed four seats. Unless the cockpit jumpseat was inop, one of the pilots of the deadhead crew should have been up there. My guess was the pilots were acting like primadonnas and refused to fly in the jumpseat. I encountered way too many pilots like that when I worked for an airline.
What airlines are required to give you when you have been IDB.
The problem is - the passenger WAS NOT denied boarding. He was thrown off AFTER he had occupied his assigned seat. Laws are written in words, words have meaning. He was removed from a flight he had lawfully boarded.
If the United crew management is so incompetent that the permitted the flight to board WITHOUT having confirmed takers for 'denied boarding' then all the guilt falls to United's incompetence.
All-caps in Internet ettiquette is considered shouting at someone. Your writing has always been very clear to me and I get what you are saying in normal words.
I could study the FARs on this, but my understanding is that this passenger was at the very least guilty of "interfering with a flight crew." There are all kinds of reasons why a crew may ask you to disembark their airplane -- maybe they are over their takeoff weight, in this case, they had to position another crew, maybe because the original crew at their destination was "dead on hours."
It might be very bad PR for United Airlines and their contracted regional airline, a cop may get disciplined, the government in China may fume, "You complain about human rights but look what kind of Fascists you are in the U.S. to one of our people." But as far as I can tell, as an airline passenger I don't have any kind of legal right to occupy a seat, even after boarding. Unless someone cites legal authority on this, I don't think it works that way.