Maybe instead of giving everyone cash, the government could provide people with a default shelter, food plan, etc.
You can go look up economics papers on Google Scholar or SSRN about the benefits of direct payments versus in-kind payments. You might worry that someone will use their direct payment and spend it on hooch, but you can't stop that: if you give them food stamps they will trade that for money and then spend it on hooch.
Food: who decides who gets what? Vegan options OK? Food allergies? Only organic?
Whenever personal decisions are left to the government, things get bad.
The problem that BI advocates see with that is that there is much greater overhead in managing a default shelter program, food plan, non-food-non-shelter-necessities-of-life-plan, etc., than just establishing and managing a single universal cash allowance plan.
Also you can always increase BI (and if everybody gets it, that is going to be a fairly popular campaing promise), but people can only eat so much food.
It has a higher overhead even with a much smaller number of people using it, because the overhead is involved in enforcing the conditions which don't exist for unconditional basic income. (That is, the overhead in existing social welfare programs is largely costs expended to prevent people from using them, either at all or in the incorrect amounts for their particular qualifications. A fixed universal unconditional entitlement doesn't have that overhead because it doesn't have that function.)
> Also you can always increase BI (and if everybody gets it, that is going to be a fairly popular campaing promise), but people can only eat so much food.
People can recieve and derive utility from virtually unlimited amounts of food (just like money), even if they can only eat a limited amount, as food is a commodity.
And as much as the point you make about the politics of raising BI is frequently made about any social benefit, I don't think there's much reason to believe its true of BI. There are quite a lot of people who are already aware that benefits have costs (both personal and social), and the people who have the most interest in focussing on the personal cost also have the most resources to bring the social costs to the public eye.
That being said, there's no reason BI levels couldn't be managed by a politically insulated group (something like the Federal Reserve), and plenty of reasons why a legislature might prefer to leave those kinds of decisions to such a body.