If you default on the payments after spending the loan, how will they collect? There's no collateral to sell to recoup the principal, and the government isn't obligated to back up the loan you took, only to keep paying you UBI going forward.

Therefore, the loan would have to be dismissable in bankruptcy. So a UBI loan basically reduces down to nothing more than an unsecured "personal loan", which is something you can get today, albeit at very high interest rates:

https://www.nerdwallet.com/personal-loans?annualIncomeFilter...