> Nothing is going to be more efficient than a UBI because a UBI does exactly the thing it's supposed to do and nothing else. There is no inefficiency to remove.

Nonsense. The former system you've described doesn't pay out to working age economically inactive people, who vastly exceed those claiming employment-linked or disability benefits in every developed country. Unlike your hypothetical example of people paying each other to do each other's laundry, these people actually exist, and needless to say transforming the system to pay out $12000 per annum to tens of millions more largely non-taxpaying people has a net cost orders of magnitude more than state bureaucracy. Most reasonable definitions of efficiency would regard it as less efficient to pay out to millions of people whose actions indicate they don't particularly want the money. (Most reasonable definitions of efficiency would also argue that it's often better to divert some of that cash towards providing additional support to people that can demonstrate a genuine need for support costing >$12000 per annum if purchased from the private sector)

So on practical grounds, it's a much, much more expensive social system than any real or feasible system with a work requirement. If you want to argue that this is justifiable because it's morally imperative that people ought to be free to choose not to work or subject to any form of state assessment unless they're foreign, feel free to make that argument. Just be aware that's the true nature of the argument you're making, and that those UBI dependents' access to the affordable consumer goods (and probably food) on a state stipend is entirely dependent on the rest of the world not being able to afford such a system to retire their own menial workers.