I was as horrified by the video as the next person, but I don't think your little thought experiment isn't relevant as the consequences of throwing someone off a grounded and in flight plane are totally different.
But back to reality, I can't speak for other countries, but in America the right to exclude people from your property is quite strong. But much more importantly, while there are many factors, the police are generally not in a position to evaluate them, and as a result they do not.
For example, if I go to a restaurant, pay for my meal, but before receiving it get kicked out by the owner (without refund) due to my race/religion/whatever, I am clearly in the right and I can definitely sue. But that's in the future. If I call the cops, they can't do anything. They can't conduct a mini, instant trial to determine if I was discriminated against and determine appropriate damages. On the other hand, if the restaurant owner calls the cops, and tells them that a customer is refusing to leave, the cops will almost certainly come and take me out of the restaurant. I can sue later, but that's it.
Edit: just adding that a United passenger has even less rights than the aforementioned restaurant patron, because as part of buying a ticket they agreed to a shitty adhesive contract, the United Contract of Carriage (https://www.united.com/web/en-US/content/contract-of-carriag...).