...and it is not it's cost.
I used to be a UBI proponent. Here is why: Contrary to popular belief, the UBI costs would be close to insignificant. But as a much bigger side-effect it would solve the chronic deflationary debt crisis (yes, deflationary!) and essentially saving capitalism from failing. Everyone would benefit, the poor, the rich and the system. That's probably the main reason why many super rich like Zuckerberg support UBI. Those who complain about too much debt and cost should rather learn about the relationship between debt and wealth.
UBI is going to be the original "helicopter money" as per Milton Friedman. The term "helicopter money" has been perverted since then as a synonym for Quantitative Easing, which is almost the opposite policy with opposite effects. Zero-interest policy and QE only worsen the debt-weath spiral.
Isn't it the next natural step to let all mankind participate in it's own achievements?
But here comes the major problem: Everyone is more-or-less dependent on the UBI sponsor and thus prone to be blackmailed. Everyone is doomed to comply with the UBI sponsor's terms. There is no way to quit and switch to another UBI donor, except by leaving the country (provided there is no NWO).
In other languages, UBI includes the term 'condition-less', which should be the key feature of UBI, but it obviously would also be the main point of failure. 'Condition-less' means everybody, even the persecuted criminals should receive UBI. This is obviously unrealistic. The media would portray a new "villain" every day and demand to cut his UBI. It is only a matter of short time until society will start discussing about whom to exclude from UBI. UBI is a freedom-booster as long as it is guaranteed to be without any condition. But when UBI includes only the smallest exception or condition, then it turns into a cage for everybody.