There are alternatives to high taxes. We could have a Georgism-inspired economic system in which the land and natural resources are publicly owned and leased from the state, but what you create is yours alone. That way, there are no "high taxes" on what you create. The universal basic income is financed wholly by the wealth from leasing everyone's land and natural resources (which is much more justifiable because land is always appropriated - never created).

> An interesting thought is to consider a world of fully mobile people - who will move and who will stay in a country with universal basic income and high taxes?

The only way you get a world full of "fully mobile people" with no barriers to relocation is if the world is one sovereignty rather than several, in which case if there is a country with UBI and high taxes, its the only one.

But lots of people -- including rich ones -- who do have the practical choice to leave or stay (though they aren't fully mobile as borders and immigration policies do erect some costs and barriers to relocation) do stay in countries with relative high, progressive taxes and strong social safety nets today. I don't see why incorporate UBI into those social safety nets would change that.

Apparently, civilization -- as opposed to the law of the jungle -- is attractive to people, even many rich people. Who knew?