The way I see it if someone really does not want to work, they'll go to great lengths to cheat the system and the government will spend a great deal combating these people. Just giving the bum money will be cheaper for everyone.
More importantly a basic income will free up people who will take jobs just because they have to. This will actually open up jobs for people who want to work hard to rise above the basic level. It will give people freedom to explore things that would not be feasible otherwise. This will generate more art, more music, new science and philosophies.
Perhaps my thoughts are too idealistic but I think its more reasonable than trying to police welfare or telling everyone to just be more bootstrappy.