It's not that debt is normal or abnormal. Debt is a way of creating more liquidity on the market. Debt is ancient. The curious thing is the huge amount of debt that exists nowadays. Of course it's unsustainable and is back by promise of governments. It's money that doesn't really exist. It's sort of like margin trading. Banks lend money they don't really have and are allowed to do so to an unbelievable extent. And this reduces the value of the money we have.