According to United’s own Terms of Service, Dao had a legal right to that seat, and United had no legal basis to eject him. Munoz has admitted as much.
Dao didn’t “fight” with anyone. The three security persons who injured him were the sole aggressors.
There is a difference between a contractual legal right and a property legal right.
What Dao and every other ticketed passenger has is merely a contractual right to a service, to be transported to a particular destination. We don't have the legal right to possess any particular airplane or any particular seat on any airplane. We don't have the right to specific performance, which is a legal term for requiring a party to follow through and perform the contract. We merely have the right to money damages if for whatever reason the airline decides not to perform their end of the contract.
Let's say you and I get on a flight from LA to NYC. Halfway through the flight the captain gets on the intercom and announces that everyone get ready to land, we are landing in Kansas City. No reason is given.
And we land in KC. All of us passengers are hopping mad. We taxi up to a gate. The captain announces that everyone must get off the airplane.
Do you and I legally have to get off the airplane? Or like Dao, can we say look, we have tickets to NYC, we are staying in our seats until this particular plane takes us on to NYC?
Of course we have to get off. IT'S NOT OUR AIRPLANE. We can sue them for money damages for not fulfilling their side of the bargain. But we have no right to sit in our seats and make security guards drag us off of United's airplane, even if United is breaching the terms of the ticket.