[jqm]

Banks (in the US) can't just lend out however much "fake" money they chose depending on how confident they are.

There is a reserve ratio that must be met. That is the percent of deposits that must be kept on hand and can't be lent out. This rate is dictated by the Federal Reserve (the central bank) in the US. Adjusting this rate allows more or less lending and thus influences inflation. So in short... central banks have a lot more control over the money supply than they themselves simply creating money out thin air.