If the income really is guaranteed, competition in UBI-secured lending should eventually drive margins down to the point where the borrowing cost approaches the risk-free interest rate, so at least people are getting a reasonable deal on their loan.
Of course, it's still a serious social problem if people borrow against their future earnings to buy expensive things and then go years without enough money for food. It might not even be irrational, for example someone might borrow to pay for a life-saving surgery for a family member.
Of course, it's still a serious social problem if people borrow against their future earnings to buy expensive things and then go years without enough money for food. It might not even be irrational, for example someone might borrow to pay for a life-saving surgery for a family member.