I'm not talking about banks being allowed to loan out peoples' deposits, I'm talking about them loaning out their own money, that they get for storing peoples' money, for example.
And a money manager could take care of loaning out peoples' savings.
If this were to happen, the cost of having a bank account would go waaaaaaay up. Right now I pay $0 for a bank account. What you're suggesting is a lot more like an investment trading account where a single stock purchase is $10. Can you imagine debit cards having a $5 or $10 transaction fee? The problem with this is that the economy is driven by spending. Anything to discourage spending is bad for the economy.
The other issue is that clamping down on the amount of money that can be lended would drive interest rates up a lot. With our current system, the pool of money to borrow is enormous, so borrowing money for something like a car can be had for maybe 2.9% interest. If there's a hard physical limit on how much money can be borrowed then you could expect that interest rate to be more like 10-20% and people only be able to borrow small amounts of money (because 20% interest on a large debt would be impossible to pay back).
