For issue (1), what's wrong with keeping a vestigial means tested welfare state around? If a UBI works as advertised, the number of people who need further assi

For issue (1), what's wrong with keeping a vestigial means tested welfare state around? If a UBI works as advertised, the number of people who need further assistance will shrink dramatically. Who cares how inefficient (say) food stamps are if, to a first approximation, nobody uses them? Besides, the existing American welfare system is ostensibly focused on providing a minimum standard of living to children, on the theory that kids shouldn't be punished for their parents' dumb decisions. A lot of the more glaringly stupid and inefficient bits are places where the relevant politicians wanted it to be for everyone in need but had to find some way to claim it was only for families without actually making it only for families. Having a UBI backing the welfare system removes a lot of the impulse to game the system and gives a lot more heft to the argument that children really should mean children and the archetypal broke 30-something bachelor actually should be on their own. Issue (2) is likely to be a fraught issue no matter where the line is, but luckily in an American context we've already spent decades hashing out the boundaries of a well defined Social Security system. Have an SSN, get a UBI; no SSN, no UBI. That's probably not the best answer, but it's probably good enough to keep relatively small immigration issues from derailing the whole project.