> > Moreover, without massive changes elsewhere in society, UBI would decrease social mobility and lead to a two-class society that keeps the poor even poorer than now.
> Could you elaborate on that a bit? How and why would it do that?
Disclaimer: I'm not an expert on UBI myself and have merely been to a talk+discussion about it, so I'm happy to be convinced otherwise or hear opposing arguments.
I see two problems. First, a realistic UBI would be at an extremely low level, barely exceeding the existence minimum. However, it would diminish employer's willingness to treat people in unqualified low-wage jobs fairly and well (in small companies they do that a lot). They would fire and hire as they see fit, because someone fired supposedly could live easily off UBI. It seems to me that a consequence of this attitude is also that wages for those jobs would sink and some of these jobs might even degrade into unpaid "internships", based on the argument that people with UBI can take those jobs to have a purpose or for personal development, but don't need them to sustain their life. In reality many of them would still depend on those jobs, though, because UBI would be too low.
Second, UBI itself does not prevent massive capital accumulation and the continuously increasing divide between rich and poor, and it does not prevent the spreading of wealth by inheritance (as opposed to merits and work). There is no obvious reason (or at least I cannot see it) why UBI would change the current trend of increasing the gap.
Taking these two issues together, I don't see how UBI can solve society's main problem, which is this increasing gap between rich and poor and all problems that come with it regarding eduction, health care, political power distribution, social mobility, renters vs. land-owners, gentrification, etc.
I'm not an economist, but Negative Income Tax seems much better to me.