UBI isn't a lefty idea at all actually. It's probably most popular with right-leaning Libertarians.

It's wealth redistribution, so I don't see how it fits with libertarian ideals in any way.

there's a far greater diversity of Libertarian thought than you seem to be assuming, and ultra laissez-faire capitalist ideology is a very very narrow slice of it that I think is a position discussed loudly by undergrads and dismissed quietly by everyone else.

The reason this form of wealth distribution is favored by many Libertarians is that it far more free of encumbrances and complexities than any other form of redistribution you might think of. It's not means-tested, everyone gets it, so that avoids the moral hazard of treating the wealthy differently than the poor. It's not restricted in what you can do with the money, so that avoids the moral hazard of picking winners and losers in the marketplace by government fiat. It's not linked to unenforceable nanny state monitoring of people's behavior, so that avoids the moral hazard of intrusive bureaucrats monitoring your spending habits.

It is a policy that can aim to provide significant humanitarian improvements in people's lives while avoiding many of traditional pitfalls of government policies intended to provide humanitarian relief.

> than any other form of redistribution you might think of.

and why do we need to do redistribution of any sort? I think that's what Libertarians are opposed to.