Sorry officer, the lesson here is...if the plane is already boarded and seated, and 4 United crewmembers show up at the last minute and need to dead-head, it is grossly inappropriate to force people off the plane to accommodate non-scheduled employees.

Lesson #2 is, in a free market economy, you continue to up the bid to buy back the seats until someone gives them up "voluntarily".  Not belligerent force and coercion as was the case here

Lesson #3, you don't physically assault someone who is behaving lawfully.  Not cooperating with police is not illegal, if the police have no legal grounds to forcibly remove you in the first place. 

This person was not being trespassed by united, you don't go hands on to remove someone to enforce internal airline policy.