The only rational argument for 'a country MUST repay its debts!' that I can make is if it is being charged interest on those debts no higher than the CPI increa

The only rational argument for 'a country MUST repay its debts!' that I can make is if it is being charged interest on those debts no higher than the CPI increase of that currency. The whole point of interest in a loan is to cover 2 points: 1) The lost purchasing power of that money i.e.: the cost of inflation over the period of the debt, and 2) The priced-in risk that the loan will not be repaid in a small portion of cases. This is why unsecured debt attracts a higher interest rate than secured debt and is why all debt incurs a higher interest rate than inflation. I don't understand why popular opinion towards debt seems to invert at some point. I'm sure if you asked these same people whether bankruptcy processes should be outlawed many would say no, but yet at some point between 'person' and 'nation state' their opinion changes without changing any of the inbuilt mechanisms for supporting that process (interest on a loan to price in risk). It's a fascinating example of once you make something sufficiently faceless, peoples' views towards it changes. See also: politics towards social classes, etc.