It's nowhere like asking someone to leave your house. A plane is not a house.
This is someone that paid for a service, is following all the rules set in contract and is not causing any problem to you. You merely picked on this person at random.
This is like expelling a tenant that didn't do anything wrong and paid the rent because you want to let your cousin sleep for the night.
It's more like pulling over at the side of the road and asking a passenger to leave your car. You are indeed quite entitled to do this. I think landlords and tenants are a distinct situation that does not apply to the rest of the business world. There, services can be terminated, or goods not provided, and the the resulting disputes are fundamentally civil.
Also, evicting a tenant so you can occupy the space is pretty much the most legitimate reason there is for eviction.
But still the eviction has to follow due process in virtually every jurisdiction.
And planes are nothing like private cars. An analogy would be Taxis. Taxis accepting the fare but then leaving passengers "at the side of the road" without provocation or reason is also against consumer laws in lots of jurisdictions.
At that time, this was the due process: ask the passenger to leave, and if they refuse, apply force. I'm arguing that this is the appropriate process. And in general I'm arguing for less regulation of how people resolve private disputes over business arraignments.
This is someone that paid for a service, is following all the rules set in contract and is not causing any problem to you. You merely picked on this person at random.
This is like expelling a tenant that didn't do anything wrong and paid the rent because you want to let your cousin sleep for the night.