Japan is not the only one, I believe China does it too. There is a merit to this, and even though i can see many people would be unhappy to give up their citize

Japan is not the only one, I believe China does it too. There is a merit to this, and even though i can see many people would be unhappy to give up their citizenship (basically, you'll be required to have a visa to visit your family, which is big inconvenience), if it's part of the deal, I think many people would still take it. Most of these though, I feel, should not happen retroactively. In other words, if they are already naturalized citizens and now have two citizenships, they should remain so. US shouldn't go after all the generations who naturalized. It's fair if they require you renounce your former citizenship going forward.