The argument tends to circle around the fact that the existing programs dis-incentivize getting off disability or Section 8 because the recipient is penalized in a step-function way (as soon as they get a job, they may become ineligible or could be charged with a crime). A well crafted UBI such that it's an income tax rebate (not to be confused with tax credits or tax deductions) to replace the many smaller safety-net / welfare programs eliminates the disincentive for people to get off these specialized programs that already exists.
While I don't think Americans are well informed enough to make a rational decision (and will likely be swayed by emotion), I think there are reasonable arguments for UBI / BIG.
[1] http://econlog.econlib.org/archives/2017/01/munger_on_the_b....