I’m certainly in sympathy with this. I think the neoclassical economist is going to argue that they can offer a straightforward utilitarian justification: namely, that in a competitive economy (e.g. an Arrow-Debreu setup) where goods like “grapes at t” and “grapes at t+1” are traded, mutually beneficial trades will result, in equilibrium, in the price ratio 1:1.5, so that the “interest rate” just falls out naturally from that price ratio. In other words, there’s nothing special about “usury” as opposed to any other sort of trade. Now I take it that what you are questioning specifically is *honouring* the trade, and that you are suggesting that there is indeed something special about there being a time dimension here which would not apply in the contemporaneous case. I suspect the neoclassical economist is going to resist all this but it certainly sounds an interesting line of attack.