If a minority of voters are dependent on the UBI and a majority decides that they do not like the system, or a politician persuades them so, they will vote against it. ("Working your ass off on lazy strangers" is a huge boon for populist politicians.)
If a majority of voters depends on the UBI and a minority is compelled to provide it to them, they basically have no recourse but to emigrate. At which point you lose their tax money, unless you impose draconic measures on emigration.
I don't see why they shouldn't be free to. Yet, weirdly, we don't see a lot of people renouncing their rich-socialist-nation citizenship to run off to some other libertarian paradise.
You can get as pedantic as you want about the definition of socialism, but the point is, there's no evidence that a program like single-payer healthcare or UBI will drive off everyone who pays into the system.
What evidence we do have says that people are not going to mass-flee a country just because taxes go up to benefit the lower classes at the expense of the higher earning ones. I therefore assert that inglor_cz's assertion is baseless. Feel free to provide a counter-example.
I have a feeling you're pedantically latching on to the word 'socialist' as a, frankly quite silly, effort to try and link the concept of higher taxes with authoritarian-communist countries. I believe you to be arguing in bad faith.
Otherwise, I can simply point out that many almost all the countries with single-payer health care are still plenty enough peopled to be able to pay for it and don't have to have any draconian policies against leaving. As I understand it, even residing outside of them often exempts you completely from taxation, which even the 'can't afford single-payer!' US doesn't do.
What does single payer system have to do with UBI? Americans also have medical insurance and they also pay for it one way or the other. The UBI tax would come on top of that. The same thing as in single payer countries. Your are not disproving inglor_cz's assertion in any way.If anything you confirmed it with an example of socialist countries.
The assertion seemed to be that higher taxes which go to universal social programs cause people to flee, I provide examples of countries that have higher taxes going to social programs where people have largely not fled even though such activity is not prevented. I fail to see how this confirms the assertion.
