This subject seems to be a confusion of issues. If a passenger insists on getting off an aircraft whilst it is on the ground then it is difficult to imagine a scenario where such a demand would not be agreed to by the aircraft commander. Nobody wants a disruptive or non compliant person on board.
The passenger would then be handed over to the appropriate agencies at that airport to be dealt with accordingly. The passenger would normally, in the absence of any overriding safety concerns, be in breach of their contract of carriage, and the airline would be within its right to seek recovery of any damages incurred as a result of that breach. In addition there may be other concerns with regard to security, immigration, or legal matters that might warrant the attention of that countries police or other security agencies.
However where a passenger wishes to disembark purely as a matter of convenience it is incumbent on the commander to point out that this is not permitted for whatever reasons may apply. The passenger is carried in accordance with the general conditions of carriage and has contractually agreed to those terms. The Captain is empowered to give instructions that ensure that the "efficiency and regularity of air navigation" is maintained, and passengers are required to obey all lawful commands given in this regard. Anyone who wishes to disembark an aircraft in contravention of those instructions would in all probability be permitted to do so, however they would likely find themselves in difficulty on a number of points.
Article 77 of the ANO 2005 states:
Authority of commander of an aircraft
Every person in an aircraft shall obey all lawful commands which the commander of that aircraft may give for the purpose of securing the safety of the aircraft and of persons or property carried therein, or the safety, efficiency or regularity of air navigation.