I don't think anyone is doubting that giving people money improves their lives. That seems to be the conclusion of these studies. However what is seemingly _never_ studied is how to finance such an operation. The money has to come out of the system somewhere. Is it with new taxation on XYZ, or slashing services somewhere else etc.
I’ve seen proponents suggest we take the money from other welfare programs, as paradoxically the means-testing overhead costs so much that we can afford to pay everyone $X instead of thousands of workers to process thousands of welfare applications. I haven’t seen specific numbers about this though. Edit: I'm failing to find numbers to support this now.
The 2022 budget was $1.2T across all welfare programs[0]. This includes programs people don't normally consider welfare such as the Child Tax Credit and parts of the Pell Grant.
There are currently 350M people in the USA [1]. $1.2T / 350M People is $3,428/person/year. Please note that while significantly less, there will still be some overhead in the UBI program so the actual number is lower.
This also doesn't include state budgets for welfare.
[0] https://budget.house.gov/press-release/7582
[1] https://www.worldometers.info/world-population/us-population...