Is it better for people to be in constant fear of poverty while being maximally productive or for people to choose to be less productive in a field they enjoy while being supported by taxes extracted from corporations and the ultra-rich?
If you were super rich and your taxes increased dramatically, what would you do? If you were a corporation and your taxes increased dramatically, what would you do? And where would this all lead? The real world doesn't always work the way we would like it to.
Let me present some more historical results: retirees. Do pensioners contribute more or less to society than before they retired? Are they a net contributor or a net drag? A UBI turns everybody into a pensioner.
The two situations are not identical, but they give me pause.