it's not possible to "create credit BitCoin out of thin air". One must consume significant processing power to find a (previously undiscovered) large number whose SHA-256 hash is below the current target.
You're thinking "BitCoin", but I said "credit BitCoin", like "credit dollars" which don't require printing dollars, just accounting.
In a free banking system (which bitcoin is, since there is no central authority), competition amongst bitcoin banks will lend itself towards 100 percent reserve banking.
There is no free banking system, nor will there be (as long as people have a physical presence) because of the ultimate centralization point: the state. The state (/ banks) has replaced gold with paper. If a digital distributed currency becomes important in the world's economy, the state would want its cut. But if the currency is able to increase its supply as the entire network decides, the state can no longer substitute cash needs with credit.
So there is no serious need to deposit your money at some bank
I have not thought for a moment about people depositing their BitCoin so that banks could lend it further. I have only thought about the state creating the laws which would allow banks to create credit BitCoin. Thusly, the state creates the inflation. This is my point. Rather than having the state do it, create the mechanisms for the peers to do it as they see fit so that they can as a whole self-correct themselves.