Thanks for this; it’s very helpful.

What I would make of your reply is that time discounting doesn’t justify ‘usury’ in this case — rather, the sanctity of the agreement does. Time discounting shows why I made the agreement, but it doesn’t show that, on purely utilitarian grounds, it’s for the greatest benefit that I honour it.

That’s ok with me, because where I want to get to is that there’s no shortcut to justifying the institution of debt without justifying the importance of keeping promises, honouring contracts, etc.