I think I evaluate calling the police a bit differently based on both experience and what I have heard reported elsewhere. But I agree this is a pretty fine judgement call in this case and reasonable parties may disagree.
I would just urge people, including airline and airport employees, to recognize that the police will often use violence when it is not really required (as it is when defending against violence). There are tons of documented cases of them abusing people and even killing them when dealing with non-violent situations or based on erroneous information.
For example, in Maricopa county Arizona the county attorney has justified the use of SWAT team raids to serve warrants on non-violent offenders because the SWAT teams “need the practice”. The use of a SWAT team dramatically increases the odds of a bad or even lethal outcome in such cases.
Admittedly a more general observation, but which does apply to this airline case. As you noted, there were lots of other things UA could have done. Indeed, there is good evidence another party was willing to surrender their seat in order to get Dr. Dao to his appointment, but it was unclear that UA ever offered the seat then to Dr. Dao.
Would that have changed the outcome. I think not given Dao’s determination
Here I guess I have to disagree. But my analysis is predicated on the assumption that UA called airport security or law enforcement (and the prior posts in this thread provide no evidence that someone other than a UA or subcontractor employee called law enforcement. Please correct me with the appropriate citation if that is not the case). Even without the offer of the other seat, they could have adopted the position that they were not moving the plane until Dr. Dao left and that they would hold him responsible, as a breach of contract, for the cost of the delay of the plane and passenger time as incidental damages to that breach, then let him deal with that. They also could have brought up a different plane (admittedly expensive but one could try to hold Dr. Dao responsible as an attempt to mitigate damages) and moved the other passengers and let him sit there. Lots of other more peaceful alternatives than calling law enforcement.
IMO a terrible example of treatment of customers by UA in any case and the reason I avoid flying them. This despite the fact that they have changed their explicit policy. I think the fact this happened shows a bad attitude about customers in their culture.