I just don't understand the police response. Not to go off on police violence/BLM/political hand grenades, but why use violence so early? They could have at least explained to the good doctor "You can sit here all day, but this plane is NOT leaving with you on it" or any number of other things to get through to him he had to leave the plane.
This is a complicated matter, particularly in the context of the modern social media paradigm. It's never black and white. In this case: United (or rather, its contracted regional carrier) was within its rights to remove passengers from the plane. They should have not boarded them to begin with, and they might have upped the incentive a bit more, considering the unfairness of boarding and then removing.
The passenger was reasonably upset, but failing to obey a crewmember is, I believe, a federal offense? So he was videotaped committing a crime.
The fact of the matter is, that with the above aside, or rather in the context of our society, most people will only see a sensational newsclip and wringe their hands before typing angry social media posts with the intent to DESTROY United. Because that's what we do now. We don't just disagree with things. When people disagree with us, or say/do things that upset us, we must DESTROY THEM in every facet. United should have handled this better on social media and merely given a vague answer of "we're looking into our procedures and working with police to resolve this type of conflict in the future".
With that being said, let the dude try to sue... he is on video committing a crime. Whether THAT is good for the company is up to their PR/Legal folks. If I was principled and he sued, I'd take him on and drain his funds in a case he'll lose.