I'm not even going to argue the merits or demerits of having a UBI system. The mere fact that certain people are confidently predicting the need for it is de-facto assurance that they will be wrong.
The basic premise is that automation is going to put tons of people out of work, burger flippers, taxi drivers, truck drivers, the UPS/FedEx/USPS-man, pizza drivers, you name it.
What's funny is that these guys, bleeding edge capitalists, the robber-barons of this era more or less can't themselves see that the economy is not a zero-sum game.
What happened every time some other kind of machinery or automation created a systemic disruption? The automobile largely killed the careers of stable-boys, feed-farmers, tack and saddle makers, but it created oil drillers, refinery workers, automobile plant workers, gas station attendants, road builders, mechanics, tire makers... and the list goes on and on, and got even bigger as cars and trucks improved. The automobile industry wound up employing orders of magnitude more people than the "horse industry" ever did.
For the sake of argument, say that automation eliminates 90% of retail, low-skill factory work, and transportation/driver jobs. And those making the warnings will naturally argue "this time it's different" (something someone always argues...) because ostensibly all the capital freed up by automation, and no more paying of wages will indeed go into new industries but those too will be automated. Fine. However, nothing is 100%, so even assuming that will be true... and ignoring that we're not even considering jobs/industries, or meaningful work someone is willing to pay someone else for that we haven't even dreamed up yet... All we need is a 1:1 replacement of all these lost jobs. Very minor, considering every other disruption in the world, factories, steam, the automobile, air travel, electricity, the Internet to date has always created an exponential growth in the number of workers needed.
That said... I don't think we're even looking at the right problem. The coming explosion in productivity and new capital from automation may create a labor shortage the likes of which we've never seen. The competition to get a warm body... anybody to accept a job might be so great that it'll make the "fight for $15" people look like pikers. Furthermore, there's few if any countries in the First World that has it's "native" population reproducing at even 1:1 replacement rate. They're only buoyed up by the fact that the Second and Third World wants to live here. What happens when automation sweeps their countries way faster (think cell phone penetration) than the rest of the "industrial revolution" did or even has to do so yet than it did in the First World and they stop coming?
Even that might not be the "right problem". What we're ultimately talking about is post-scarcity. We've never ever had that in human history. We don't really know what it will be like. We could even see ourselves in such bizarre circumstances as an economy that runs in reverse. Where the consumers/users are paid to do so.
