So I like Caplan's argument that social welfare programs make unemployment more palatable. But his justification of supply and demand ignores social pressures which encourage employment over jobless welfare use. I don't that's an insignificant impact. In fact, I think it's probably one of the main factors in the decision.
And if you have a floor amount of money where it is 'worth it' to take a job and dedicate your time to employment, then Wal-Mart benefits from that floor being otherwise occupied by government programs. You can prove this the same way he 'proves' his theorem, which is to ask 'If I was in charge of Wal-Mart, would I encourage a social pressure to take employment even when the pay is not at the level which produces a meaningful wage?' Of course I would, because then I can pay less as the worker gets an less tangible, but very valid, value of respect and participation in the employed labor force.
Another example on another end of the employee would be a retiree who takes Social Security. It's available to workers and non-workers, but Wal-Mart wouldn't have access to a group of workers that they prefer to hire in that position (nice old people) if those old people were still working in the job that they otherwise were able to retire from with the aid of social security.
The EITC is our greatest hope of a UBI in the near future. And was actually the idea of the EITC in the original Friedman plan, which he called a 'guaranteed income.' There's better sources than that, but his book (which is like Gospel to me) is harder to link.