Wrong in this case means using violence when it was not necessary.

This seems to be the standard that you're using to condemn the passenger. Why are you not applying that standard to United as well?

Note that, if we accept that violence is acceptable to remove a noncompliant passenger, then violence was chosen (at least as a potential outcome) the moment that United decided to remove people involuntarily.

Why do you insist that "it is" childish behavior from a professional adult, exclusively and ignore the behavior of the airline, which brought violence into a situation that did not call for it?

This is why I don't say that you're wrong, but that you are being extremely one-sided. You continue to attack the passenger's behavior while ignoring or outright justifying the airline's behavior.

The passenger should have complied, and the airline should never have put themselves in a position where they might have needed to threaten force. Do you not agree?

If you do agree, then understand that people focus more on the airline for some really good reasons, namely that they started it, and they wield all of the power. We place more responsibility on entities which start something than those who merely respond, and more responsibility on entities with power than those without.