Just because you might touch down is NOT usually a reason to refuse a go-around. We get those situations quite often in the simulator, and touching down is NOT a criterion in a successful event.
Remember that in the case of a "balked landing" (the official term for a go-around with a touchdown) you are at flying speed immediately on touchdown, and the engines are already spooled up. With all engines operating, there is usually no concern about climbing out immediately. If you would consider a touch & go on the same runway, there is no reason to fear a balked landing.
I agree! Even after a landing clearance a go around negates that clearance.
It could be that a vehicle enters the runway at an intersection point meaning that to continue the landing would result in a collision.
A go around on touchdown is part of the training and not a big deal at relatively high speed.
Obviously the Captain has ultimate authority for the safety of the aircraft and PAX but ignoring or overriding a Go around instruction will mean he will have to explain himself after the event.
That explanation would determine whether his decision was correct or incorrect or in a grey area. He could face charges for ignoring an ATC instruction and if a collision occurred because of ignoring a go around instruction It would be hard to justify that decision .