it would completely obliterate poverty in the US.
Not really, it would do little to help people in poverty already past 18 (unless they had children who were both just about to turn 18 and those children were generous...). Even for those that benefitted from this, to assume they would not go back to poverty you have to assume they will use it wisely (and possibly have some luck too.) If they go to college or start a business with that money, then they probably will move up and sustain themselves at least in the middle class. Probably. On the other hand, I bet a large percentage would spend it quickly and have relatively little to show for it at the end.
Even those who start a business/go to college are not gaurunteed to stay in the middle class, they just have a good shot. Many businesses fail, and then those founders would be left with little but that experience. Many people with degrees are unemployed right now.
I am not saying it is a bad idea necessarily, and I am certainly not about to dismiss it as stupid, but I do not think it will come close to wiping out poverty.
Professional football players make a ton of money, and guess how many end up filing for bankruptcy within 2 years of retirement: 78%.
http://sportsillustrated.cnn.com/vault/article/magazine/MAG1...
I know that adding rules makes things more complicated and can have unintended consequences.
The US has a population of, let's say, 300M. In any year, let's say 1/60 of that many -- 5M -- are just turning 18, which is when Bowles proposes handing out the money. (He's not proposing to give that much to everyone all at once.) So the annual cost is $250k times 5M, or about $1T. There's no $56T up-front cost.
Now, $1T/year is an awful lot: it's about 1/4 of what the US government currently spends in a typical year. It's about what the US government currently spends on "defense". It's hard to see where the money could come from. On the other hand, it would completely obliterate poverty in the US. On the other other hand, it's very convenient for a lot of people that there is poverty in the US; without poverty, no one would work for very low salaries, which means a lot of things that are currently cheap would become more expensive. (You can generally recognize countries with less income inequality because low-end goods and services cost more.) On the other other other hand, it does seem like it would make entrepreneurship much more widely accessible.
Bowles is a very smart guy. The idea may be crazy, but it's unlikely to be stupid.