Y'know what? That's fair.
My understanding has been that the entire point of a progressive tax system is to sap money from the wealthy and redistribute it towards the public good. Whether that system works is debatable, sure.
Point being, actual UBI would require significant tax hikes and closing of tax loopholes which predominantly target the wealthy. While that may lead to capital flight, it's not a bad thing. As a whole, UBI wouldn't be a small step but a massive stride towards achieving socialism.