This is a red herring. It's easy to assuming that such an enormous undertaking can be solved by "tax the rich". It doesn't work that way. There isn't enough money in the top 1% of the United States to pay for such a program. Inevitably a UBI would be paid for by the middle class, the meaty part of the bell curve.
This means people who took on debt loads to become a doctor, lawyer, whatever, and have worked hard to pay it down (and probably still are paying it down). $250k/yr sounds like a lot, but when you're paying back $400k worth of loans, it's really not as exorbitant as it sounds to many people -- especially if these same people are trying to buy a house, save for their kids' college, etc.
Global economic output is $80 trillion. There are 100s of millions of scientists, engineers, programmers, technicians in the world. Aside from the ideological complexities, which are probably intractable, it seems like it would be pretty easy to me.
What would it really take to provide basic housing, food, water, clothing, energy, and medicines to 7 billion people? Robotic automation, free / cheap energy, and access to natural resources.
The difference is that the owners of the capital aren't willing to lose on their investments, and it's cheaper to bulldoze and throw away than to give it away or provide work maintaining the communities that these properties exist in/on.
People can do whatever they want to their property, no?
Do you personally allow homeless people into your house?
Problems you mentioned are real and tough, but the objections are very simplistic. Its very easy to demand others to do something, and distance yourself away.
There is a long and historical precedent for demanding that people with excess amounts of capital owe a greater portion than those who own relatively little. There are material differences between the capitalists and all the rest of us, and those allow us to demand specific concessions from them.
The technology to bring about a post-scarcity world mostly exists, and we could get there very quickly (maybe 5-10 years). But, how do you convince the upper classes (who control the capital) to support it? How do you temper the common idea that 'the lazy people' will just do nothing all day? (like that's a bad thing)