It's not the system that's wrong, it's the people trying to achieve personal gains with it.
Debt-based money is unsustainable because it requires an exponential growth of the money supply: when money is debt, paying interest on this debt requires creating more money, hence more debt.
Money was debt-based from the beginning. When the tax debt to the state mafia was payable in barley, then barley was money. When it was payable in a specific metal, than this specific metal was money. The interest rates in ancient mesopotamia were much higher then today.