Oh my God, to abandon U.S. citizenship voluntarily is called a “relinquishment” under U.S. law, specifically, section 349 of the Immigration and Nationality Act. The practical effect of it, since 2008, has been that a large number of people who are deemed U.S. citizens will actually be subject to an exit tax, whereby all of their world assets are, first, identified, and then second, there is a deemed sale of those assets and they have to pay a capital gain on money they've never received. That's only for the property. If it's a pension plan or something, the full thing is valued and deemed paid out.
That's not for everybody, but applies to people who are called “covered expatriates”, those who have a net worth of over $2 million, which realistically is an awful lot of people in major urban areas who are in their fifties and sixties. Or, significantly, these are people who cannot demonstrate five years of U.S. tax compliance. Since a lot of these people didn't even know they were U.S. citizens, they're obviously not tax compliant, so they're hit with the absolutely horrendous cost of that five years of tax compliance, which may be more than taxes and penalties.
It is an unbelievably expensive undertaking. You do not leave U.S. citizenship for free—