This has come up in several posts. I believe that UAL management had no time to gather all the personnel related facts before allowing the flight to continue and relied upon the acceptance of the continuing crew that the flight could operate safely with that crew.
If UAL management polled the crew and received assurances from them without undue pressure or coercion that the flight could continue safely on to Chicago with Queeg still at the helm. Then I would be happy with that explanation.
Put simply, there has been a diversion for whatever reason, the pax / crew are then processed in accordance with procedures by the authorities. Customs might wonder about it all, but speak sternly to the Captain about a decision (right or wrong) to divert or to be angry about it, I'm not convinced about that.
Immigration and TSA on the other hand ...
I'm sure the captain picked MIA for its 24 hour, 1hr notice customs availability over the more onerous requirements for landing at MCO out of normal hours in the middle of the night, where United has a base. But as the captain appears to have received the documents he demanded and with no prospect of an ugly face to face confrontation with the purser unless the captain chose to initiate one, I can see no justification for the captains actions. That the rest of the crew, US customs and TSA were able to accomodate the diversion with the minimum of inconvenience to passengers does little to mitigate the captains strange decision and the still significant inconvenience suffered by the passengers and the government agencies tasked with processing them, nor the damage necessarily incurred to UAL's reputation or the significant costs involved. Sure, let's try to keep an open mind until all the details are in. But I'm having a hard time justifying the diversion, short of some percieved threat to the continued safety of the flight which only the captain seems to have been cognizant of. In short, not looking good for Queeg.