I believe there is an exit tax when expatriating from the US. As best I can tell it is calculated on a “deemed sale” of a person's assets on the day before their expatriation. I'm not very informed on this topic. Just saying that throughout your life you're opting-in and opting-out of various systems (sometimes actively, sometimes passively) . There may be a tax/cost to opting out, but if it's tied to the moment of opting out that seems like a roughly reasonable way to organize society.