He has every right to remove a passenger who is causing a disturbance or presenting a threat.
He doesn't have the right to because the airline wanted them off in breach of the contract of sale and the guy said "yeah no".
Refusing peacefully to go along with the fiction the airline has created isn't causing a disturbance. You can't force someone in to a "disturbance" state if they're just sitting there。
Look, involuntary bumping happens on every airline every day. The fact is that you don't have a right to fly if the airline or captain doesn't like you for any reason (aside from protected discrimination classes, like race or gender)
Why should the captain have every right to remove a passenger? Should that include the right to remove a passenger because the passenger is Jewish? How about because the captain wants that seat for a set of golf clubs? That's what you said, and I disagree. The captain isn't God and aircrew are constrained by laws just like everyone else, no matter what the airlines would like us to think.
The captain has every right to remove a passenger because, he is not supposed to fly unless he is feeling safe to fly, he mustn't, and it is assumed that letting 200 passengers fly safely is more important than letting one passenger remain "innocent until proven guilty".
That said, the captain's decision does not make him immune to lawsuits, disciplinary action, etc. but on his plane, especially while flying, temporarily he IS god.
Ahh. I'm guessing he has complete rights to not fly, but I don't know if they have rights to physically remove a non-aggressive/dangerous passenger. I of course don't know the law.