Even at first order, it makes the people at the bottom relatively better off. If we go from Alice having 600, Bob having 0, and Carol having 0, to Alice having 700, Bob having 100, and Carol having 100, then Bob and Carol are still more able to buy things than they were before even if prices now increase by 50%.
The arguments against UBI are pretty much the same against rising minimum wages. That being, the baseline just moves, so everything gets more expensive, so the situation doesn't improve at all.
It intuitively makes sense, and like most economic reasoning it's horribly simple. But economics is comprised to two parts: theory, and practice.
Practice always trumps theory. If practice defies your theory, it doesn't mean that the market is broken, or that there's over-regulation, or that your theory will eventually come true. It means your theory is just wrong. All economic theory are predicated on thousands or millions of underlying assumptions. If even just a few of those are not true, or aren't true in the way you think they are, then the theory can be wrong while simultaneously being logically perfect.
When it comes to the arguments against minimum wage, the theory is just wrong. Rising minimum wages do help people making minimum wage. If it does raise the COL, it's slowly, and not in the same degree as the minimum wage shift. In addition, a flat minimum wage still results in a rising COL. You can't simply pin the COL like that.
So knowing what we know about minimum wage, I think it's arrogant to claim the UBI would just result in a rising COL to eat up all the UBI.
