IMO the problem is that reducing incentives to work makes it hard to compute the actual cost of UBI. Naively, if we want to pay each person a UBI of X, all we need to do is multiply X by the size of the population. We can then infer how much it would cost to each given taxpayer. But, because of reduced incentives to work, there are additional effects s.t. reduction in tax revenue and increase in the price of labor (that propagates to other prices). The latter means we don’t even know the value this X will have to the recipients.
IMO the problem is that reducing incentives to work makes it hard to compute the actual cost of UBI. Naively, if we want to pay each person a UBI of X, all we need to do is multiply X by the size of the population. We can then infer how much it would cost to each given taxpayer. But, because of reduced incentives to work, there are additional effects s.t. reduction in tax revenue and increase in the price of labor (that propagates to other prices). The latter means we don’t even know the value this X will have to the recipients.