Yes the passenger has a right to demand to get off, but by doing so, he may cause a delay for a security check that he has not left anything on the plane. This would lead to loss of a slot, and a wait for another. Maybe on a time critical flight, the crew may not be able to complete the duty and be replaced, involving at least a further 2 hour delay, maybe an overnight if there is a night curfew, with hotel transport and wasted catering and cleaning costs. 747 delays are priced at over £100 a minute including disruption costs- if hotels are involved, the costs will quicklybe astronomic. I think you will start seeing aggressive recovery costs being sought from the individual 'demanding HIS rights' whereas airlines don't really bother now.
So how do the 'rights' of an individual who freely bought a ticket stack up against the 'rights' of 350 other people to go on the journey without undue delay that everybody bought a ticket for? There's too much emphasis in society on personal 'rights' without any thought that there is also personal 'responsibility' not to make a nuisance of yourself to your fellow man! I would have no hesitation in going to speak to the individual, and allowing all those around to know that they aren't going anywhere and why and who is responsible- it would be unavoidable. I would expect the passengers to find an adequate 'solution'!