The only way to pay interest on all debts is by creating more and more money.
Yup. Just the interest payments on our debt cost us half a trillion dollars a year. And since debt is increasing, interest payments will increase too. It won't be long before interest payments become one of the largest outgoings of our government's budget. And what happens then? When we pay more on interest than we do on military or healthcare? How much money do we have to print then? How worthless does the dollar become? Or do we just renege on our national debts and let the whole thing collapse?
Either way, the outlook for fiat is bleak.