It is the manner of the removal that is the problem.
They should have gotten actual police officers to remove Dao, not security guards with no experience and no arrest powers.
UAL probably thought that the officers who responded were police officers. Unfortunately, they weren’t.
I agree.
Law enforcement could have said, you are now down to two options.
option 1, you leave on your own power and can then seek what ever redress you desire
-OR-
Option 2, you leave under arrest and face criminal charges.
This is the default option and if you do not leave on your own power, by the time you are asked to leave for the third time, you will be automatically processed under option 2.
How would you like to proceed?