We already have the massive wrench in the form of benefits programs and EITC, etc. I say: restructure them to be UBI instead.
Milton Friedman advocated for a negative income tax which is much like a UBI, and most economists agree that giving out welfare in this means-tested way is extremely distortive. Maybe all these economists are "extremely credible": https://mitsloan.mit.edu/ideas-made-to-matter/negative-incom....
> If UBI proponents ran on the platform of "eliminate all welfare and replace it with UBI" I would probably support them.
I favor not quite this. I favor "eliminate most welfare and replace it with UBI". It will cost more, but it will also benefit a larger slice of people.
The proposals from the farthest left generally have UBI mutually exclusionary with receiving other benefits (from Yang et al.). So even there, we're talking about mostly eliminating other welfare.
In any case: refusing to discuss good ideas because we don't think they'll be politically tenable is a recipe for them to remain politically untenable forever.