Surely if you are saying that if you have sworn allegiance once, even to a constitution or flag,then that should do for all time, (and there is a grain of logic in that),then you must be saying that no person should change their nationality, get divorced, etc last year 16,000 people took British Citizenship which I assume would include some statement of loyalty to the Crown and to the UK, whether attested to or sworn by Oath,this does not make those people dishonest or their promise or word worthless,people always have the right to change their loyalty to anything, even their country or commonwealth cannot be taken for granted, as it will depend on the circumstances, I am quite sure that there were many Germans during WW2, who could no longer support nor feel allied to the atrocities their country was doing, the same in other parts of the world. Circumstances and people change, eg: Brexit,