Look at it from the cost effectiveness point of view. For instance, currently we have a problem with several thousands of children illegally crossing border into the US. To solve this, 4B$ has been requested. This amounts to a million per child, roughly. I could think of alternative proposals: e.g a voucher for 10k$ to the child's family, payable in a year if they demonstrate up-keeping the child: sending it to school, etc.

The 'guaranteed income' is much trickier than that, of course, but the question is still valid: can it compete on cost-effectiveness with the current system of Medicare/medicaid/SS/WIC/.....