New York University professor Lawrence Mead identified the chief flaw with both the libertarian and left-wing approaches to fighting poverty, either through existing welfare programs or through a UBI: the "competence assumption." This is the presumption that the intended beneficiaries of government anti-poverty programs always "behave rationally enough to advance their own self-interest." We all know enough people in our own lives (never mind what we know about ourselves) to realize this isn't always the case. Lots of folks are determined to do things that aren't in their long-term self-interest.
The problems afflicting many poor people are often of their own making, at least in part. Having children before getting married, dropping out of high school, etc., are transparently bad choices that millions of people make. (Also, some anti-poverty programs create incentives that make bad decisions seem rational.) But many poor people have just had rotten luck. There's good reason to believe that, with a little help, they can work their way up the economic ladder. And for countless others, the truth probably lies somewhere in between.
For 50 years, we've run a massive experiment around one approach: that bureaucrats and social planners can fix the lives of others by telling them how to live. For some it's worked, for others it's been an abject failure. But few can claim it's all been a smashing success.
Perhaps a compromise can be worked out. Why not give poor people a choice? They can stay within the rat maze of the current welfare state, or they can cash out. According to Rector, 100 million Americans receive aid from the government at an average cost of $9,000 per recipient. Surely some of them are equipped to spend that money better than the government. Why not give them a shot at proving it? If they fail, they can always switch back to the old system. If they succeed, well, that'd be a real victory in the war on poverty.