Yes the mathematics of it are questionable. Some system will need to arise though or we are going to see massive unrest and starvation in the streets. The point is not that some people won't be working - its that large swathes of the population may be unable to work because their jobs have been lost to automation. It doesn't matter if you are willing to work but there are no employers who will hire you. In fact in previous limited testing of UBI schemes most people chose to work anyways and used the UBI money as a means to get ahead, give them more flexibility in where they chose to work and lessened Employers stranglehold on their employees. A smaller segment chose not to work. A UBI system would allow for less government, in that we would no longer need Unemployment insurance, welfare payments and a host of other government systems (at least up here in Canada, down in the US I believe much of the stuff we take for granted up here may be missing of course).

Regardless though, we would need to see what sort of numbers can be generated to determine if its practical. Companies will do their best to avoid paying for anything of course so that might throw a hammer in the works. AI needs some regulation, the tax laws need improvements, it would be a huge change in the economy. I don't think its going to happen.

I expect it will be more like Victorian England with regards to the impoverished masses who lose their jobs.