The UBI would probably be fine at first, people just supplementing lifestyle and alleviating poverty. But over time the stigma from leaving workforce and doing nothing would erode. Then eventually everyone just lives in a 1BR apt and plays video games all day, or works part-time and you get less production/innovation from the disincentives.
Social security and medicare help lift people out of poverty but they also told an entire generation that younger workers would pay for their retirement so they didn't bother to save as much much.