One of the issues with UBI is it contrasts with another societal goal. Fast forward 30 years, and say UBI is the way most people live. Then the best way to have a nice family income is to have as many children as possible (since each person gets paid more). That means more consumption, more pollution, more people. AI resulting in less income for people means people will have less children, and the population will shrink, IF those people do not find alternative work. The same things were said about the ATM machine, the Steam Engine, and calculators, computers, and (believe it or not) the printing press. If and when it does become a problem of actually displacing the total number of workers, the population will shrink accordingly to account for the oversupply of people. It's a self-correcting problem over the long haul. That will likely mean two people will have one kid, halving the following generation, while still have everyone represented genetically in the future. UBI itself, is a terrible idea, because you're basically asking for a sheep farm where the sheep dont get sheered or eaten. It just ends up in an explosion in the amount of muck you have to deal with.