Oh not this again. First of all, Friedman advocated a negative income tax as a replacement to the ad-hoc mess of redistributive taxes, grants and welfare programs that exist now.
Yeah, and? He thought it was the best solution to the problem. See above about the difference between political theory and political reality.
Second, this doomsday scenario of 50 million people waking up one day to discover..
Don't give yourself a hernia setting up those straw men. No one said anything about people "waking up one day" to find themselves unemployable. The discussion is quite clearly about a problem that develops in the long term.