Yeah, but that only works if you view your citizens as your "property" that works for you and doesn't move in and out of your country. If you view them as auton

Yeah, but that only works if you view your citizens as your "property" that works for you and doesn't move in and out of your country. If you view them as autonomous agents that move between jurisdictions to optimize their benefits in their current situation it doesn't. For example (as a German citizen) you can go to university in Germany for free and move to a low tax country afterwards for work. When you are old and fragile you come back and use the healthcare system since your foreign insurance becomes too expensive (I'm not entirely sure about that loophole, but I heard it existed). Of course there is some friction involved (friends, family in the home country). But which percentage of the population has to act rationally for the system to become unsustainable in the long run? Most countries haven't adapted their policies to the reality of globalization yet. I fear some might go the way of the former GDR and try to keep their citizens from leaving. I heard even the US is doing something like that, it's said to be quite hard to get rid of a US citizenship (and the IRS).