And I think it is a fairly core UBI argument that UBI could be paid for because people would be getting say, $1000/mo cash, and wouldn't need, for example food stamps, and other cash benefits.

And what happens to people who squander their UBI? Say they take their monthly UBI deposit, go to the nearest casino, bet it all on black, and lose... Are they just left to rot and die at that point?

The entire point of things like section 8, SNAP, etc., isn't the government trying to control people's lives... Its the government providing for people who can't/won't provide for themselves... The money/vouchers given in those programs literally cannot be squandered because they can only be spent on those specific necessities... That's why they are called safety net programs, not 'free money from the government', they are meant to be the last resort to protect you when you have nothing else. A UBI wouldn't replace that unless you are ok with people who squander their UBI being left to die.