An observation, probably my last one.
I don't believe any pilot who has commented on this thread has said he/she would have acted similarly given the circumstances described. (I believe there was a comment or two that if the continued safe operation of the flight was compromised, e.g., cabin crew became intoxicated, they would divert.)
I don't believe any poster has cited a similar situation having occurred elsewhere in which disrespect, insubordination, or failure to follow a Captain's command has led to an in-flight diversion. Numerous instances cited of conflicts being handled on the ground before or after a flight, or in-flight by relieving a F/A of his/her duties.
IIRC, the time from when the CA did not promptly get the document he sought and it was slid under the door, and the time the plane landed in MIA was about five hours. Usually, sufficient time for the heat of the moment to have cooled, and calmer heads come to the fore. Allegedly, a FO suggested that if the CA was going to divert, that they divert to Orlando which was enroute and where United has a station. The CA declined this suggestion.
So a highly unusual incident, indeed it meets the definition of unique. And leading to this perhaps not-so-hypothetical question: what if United management asks this captain if he can guarantee that this won't happen again, and he replies, he can't guarantee that. With such a response, would United put him in the front seat of an airplane ever again? ---Or is he pensioned off?