There've been brief periods in US history where that was true (where the savings rate was negative), but that usually been when there's been an economic downturn [1] in the wake of stronger economic times, and in any case relies on credit availability or savings to make possible.
A drop in guaranteed minimum income or basic income doesn't mean welfare automatically reappears, it means that the standard of living drops for those dependent on the GMI/BI. But that's what you'd expect in a broad-based economic downturn -- the mean standard of living drops.
(Even if you keep GMI/BI at the same nominal level, lower productivity will increase the inflationary effect of GMI/BI, which will have the same net effect as cutting the nominal level -- its just that price levels will go up rather than payments going down.)
[1] which may include an "effective" downturn for most people during what is in aggregate terms an expansion, but where narrow distribution means that most individuals/households are making less with a small class making all the gains.
Translation: The poor can no longer afford food, because there's no welfare program and their guaranteed minimum has dropped.
Maybe they entered into a predatory loan situation where they can't simply break their contract and have to keep paying a monthly minimum, so there's not enough money for food + payment each month.
Maybe it's a standard loan situation, and now their car is repo'd because they've missed a bunch of monthly car payments. "Just sell the car and get a cheaper one!" Nobody's buying it because the economy is in a downturn, which is why the guaranteed minimum dropped in the first place. So now they can't get to whatever employment they decided to have for themselves, which further reduces their income to a level that they can't even afford food. And then there's no welfare program to turn to. So now their family is in an oh-crap situation and there isn't any government solution.
There are all kinds of corner cases which the current system handles. Any new system has to have fallbacks so that the poor can still feed themselves. Not "feed themselves in an idealized scenario where they don't have any existing debts."
> There are all kinds of corner cases which the current system handles.
Poor people not being able to afford adequate food during an economic downturn -- or even an economic boom -- on their own (including with whatever government assistance is provided) isn't, however, one of them. During good economic times, some of that gap is covered by private charities (especially for the poor in relatively affluent areas), but (1) that goes away during economic downturns, and (2) that's not something that BI/GMI replaces, anyway.
Sure, lets question if alternatives to the status quo do what we want, but lets also not pretend the status quo does things that it doesn't.
And yes, I'm pretty sure that the USA is the only country in the world where "People usually live slightly beyond their means".
^ Citation needed. Maybe it's become common since the advent of easily available credit, but for most of human history it was physically impossible to live beyond your means.
That decision would have lots of consequences. People usually live slightly beyond their means. Decrease their means, and suddenly the majority of your population is living way beyond their means.
Any guaranteed minimum income can't ever go down for this reason. You could try to drop it, but then you'll wind up paying them the same amount anyway in welfare, because many more people will be seeking welfare to supplant their missing guaranteed income.