Where will this basic income money come from? Forced taxation, aka extortion, aka partial slavery. That's not a free society, just a different master.
Also monetary freedom is only one subset of freedom. Being able to pick where and how much you work are valuable too. If we assume that due to taxation we play monetary zero sum game, giving more people choice on what they work increases total freedom.
We can also put taxes on corporations instead of people. Corporations are not humans, and therefore cannot be made slaves.
Ah, we have found the key contention. 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?
What you "earn" is partly due to your efforts, and partly due to you utilizing the infrastructure of your employer. So a part of your "earnings" is employer's.
You are being forced to brush teeth by the same entity, that forces you to work, so in this context even teeth brushing becomes "teeth brushing slavery".
While UBI itself can be managed so as not result in runaway inflation (and, unless you deliberately build a positive feedback loop into the level setting, should be self-limiting to avoid that in the long term, though the wrong initial setting could have high short-term inflation), monetizing the UBI, like monetizing government debt, is a great way to produce high average inflation, destroy government creditworthiness, and increase volatility in the currency.
If you want to redistribute downward, taxing the wealthy directly is a lot more sensible than monetizing spending. And, in any case, none of the people that are opposed to taxing the rich are going to support monetization, and plenty of people that do support taxing the rich are going to oppose monetization, so it doesn't even make sense as a way of getting around the political difficulties of tax-supported UBI.