I'm sorry but in no where there does it say to ignore airport TSA officers and make a scene.
And that's why this is sort of a hard story to take sides on.
You feel bad for the guy, but at the same time, rules are rules. If the police come to remove me from my car, an airplane, or anywhere for that matter, you better bet that I'm going to do as I'm told.
Fighting with law enforcement only creates more problems. So while United handled this poorly, the way that guy behaved is unacceptable IMHO.