I find it hard to believe that someone could live off $12k. Then again I live in Australia where cost of living on the whole is fairly expensive. But given rent is a big component of cost of living I'd hazard a guess that this will vary quite significantly in different parts of the USA. Furthermore I'm sure there are many different ways to define the poverty line. Even if the basic cost of living is met, there are additional costs that one may have to bear before gaining employment, including education, appropriate clothing, transport and the additional costs of accommodation close to employment.

The argument for a basic income is that one should be able to live comfortably and not just cover bare essentials. This means that people shouldn't be living at the poverty line but well over it. This shouldn't be a disincentive to work because most people need to live their lives around some kind of structured activity. Though it does mean that if there is a shortage of jobs then the unemployed won't be left to rot and the option exists to do some meaningful volunteer work.