I found this to be an amusing discussion:
Suffice it to say, while I am most certainly not a libertarian, it is interesting to see how one can justify certain social welfare policies from their principles, many of which at first seem reasonable. It’s amusing to see a libertarian actually grapple with questions of implementation, no matter how theoretical. Nonetheless, any philosophical justification of a basic income policy and defense of one in practice is worth understanding. If any of the theories currently floating around about stagnation and/or technology driven unemployment are true, a guaranteed minimum income is the sort of policy that will need to argued and enacted.
On the practical questions, I agree with this author. Immigration imposes one problem (though one curable, perhaps, by visa auctions or a denial of benefits for a certain length of time after moving to the US); Cowen and Manzi’s description of the implementation problem strikes me as far more damning.