A different argument against Universal Basic Income
I grew up in socialist East Germany. Like most of my fellow citizens, I was not permitted to leave the country. But there was an important exception: People could leave after retirement. Why? Because that meant their forfeited their retirement benefits. Once you took more from the state than you gave, you were finally allowed to leave. West Germany would generously take you in. My family lived near the main exit checkpoint for a while and there was a long line of old people most days.
And then there is Saudi Arabia and other rentier states. Rentier states(https://en.m.wikipedia.org/wiki/Rentier_state) derive most of their income not from their population. The population gets a lot more wealth from the state than the state gets from the population. States like Saudi Arabia are therefore relatively independent of their population's consent with policy. A citizen who is unhappy is welcome to leave, or to retreat to their private sphere and live off benefits while keeping their mouth shut - neither of these options incurs a significant cost for the state.
I think these facts are instructive in thinking about Universal Basic Income. I want to make a point that I haven't seen made in discussions of the matter.
Most political systems (not just democracies) are built on an assumption that the state needs its citizens. This assumption is always a bit wrong - for example, no state has much need of the terminally ill, except to signal to its citizens that it cares for all of them. In the cases of East Germany and Saudi Arabia, this assumption is more wrong. And Universal Basic Income makes it more wrong as well.
From the point of view of a state, there are citizens who are more valuable (or who help in competition with other states) and ones who are more of a burden (who make competing with other states more difficult). Universal Basic Income massively broadens the part of society that is a net loss to the state.
Now obviously technological unemployment is likely to do that anyway. But there's a difference between answers to that problem that divide up the available work between the members of society and answers that divide up society into contributors and noncontributors. My intuition is that UBI is the second kind of solution, because states will be incentivized to treat contributors differently from noncontributors. The examples are to illustrate that a state can behave very differently towards citizens if it is fundamentally not interested in retaining them.
I go along with Harari's suggestion that the biggest purely political problem of the 21st century is the integration of the economically unnecessary parts of the population into society. My worry is that UBI, while helping with immediate economic needs, makes that problem worse in the long run. Others have already pointed out problems with UBI (such as that in a democracy it'll be impossible to get rid of if it is a failure) that gradual approaches like lower retirement age, later entry into the workforce and less work per week don't have. But I reckon that behind the immediate problems with UBI such as the amount of funding it needs and the question of what it does to the motivation to work, there's a whole class of problems that arise out of the changed relationships between citizens, states and economies. With complex networks of individuals and institutions responding intelligently to the changed circumstances, a state inviting its citizens to emigrate may not be the weirdest of unforeseen consequences.