> However, I raise another point, wouldn't then these people who are made jobless due to technology, etc. be again powerless and unable to stop tyranny or autocracy in a without-UBI scenario [...]

I think this is a pretty good point. It's possible that UBI basically just delays the inevitable, if you believe that there really is a possible future in which most people are just economically irrelevant due to mechanization, etc. With UBI, you get a few more years before the small number of people at the levers of power harden their attitudes enough to stop the handouts; without UBI you just starve immediately. Either way, it doesn't look good.

Personally I don't think that the premise, of large-scale, structural unemployment due to automation, is really likely -- I think that "work" can expand to fill the available labor pool, with some amount of incentivizing, and a large pool of unemployed workers is threatening enough to most governments that they'll pursue economic policies to employ people, even if it's WPA-type projects, rather than endue the destabilization of having them just sit around.

As various others have pointed out, if you look at "work" today, it would be largely unrecognizable to someone from the mid-19th century. The amount of modern labor necessary to live a reasonable lifestyle by mid-19th century standards is quite low (it's hard to do this on an individual basis, but if you were to take a bunch of people and modern technology, particularly agricultural machines, but reduce expectations for standards of living to that of the 19th century, you end up with a whole lot of spare time). But yet few people do this. In fact the only people I know of living 19th century lifestyles by choice are people who actively reject modern labor-saving technology (e.g. Amish and other orthodox Mennonite traditions).

Someone from that era might justifiably question why people are still working 40 hours per week, rather than just working, say, 10, and adjusting their needs downwards accordingly. It's a fair question (and there are a lot of barriers to doing it, e.g. provisioning of health insurance). I do know a few people who have done that, in fact, and they seem to like it. But I have doubts that it will ever be an especially popular choice.

So my guess is that while automation will be disruptive, and if not managed correctly it may result in some (perhaps many) people finding that what they've spent a lifetime training themselves to do is no longer necessary -- an outcome that I think government should work to avoid, the economy will figure out ways to use the surplus human capacity freed up by automation as it always has.

There are lots of automation-resistant fields where people can essentially pay each other for services, sloshing money around and keeping everyone employed, even as a smaller and smaller fraction of people actually work in "primary industry", extracting resources from the environment or growing food. That's a transition that's ongoing already in many developed countries, and it doesn't seem grossly unsustainable except where it runs up against opportunities for arbitrage against less-developed economies at the expense of both sets of workers.