Unfortunately, I have 2 problems with this:
1. Of the people that I see in SF who could use UBI, almost none of them seem the type who would clean up their acts with UBI. They have serious mental issues, and money means only 1 thing to them: a means to chemical substances. So what do you do when a guy blows his $2000 monthly stipend on hookers and blow and now is back on the streets? Arrest him? Send him to jail? Put him in a mental hospital? And who pays for that? And who provides him the services, if the bureaucrats who used to do it are gone?
2. What do you do about the millions who are employed in the service-providing sector (bureaucrats, non-profits, etc.) ? Right now they make decent money; you're now going to lay them off. Where will the jobs come from for them?