The capital gain on housing then becomes a self-reinforcing loop as capital seeks yield in a low interest rate environment, and investment flows towards these unproductive assets instead of creating productive capacity. Regular buy-to-inhabit buyers are dragged along in the cycle as long as they can obtain sufficient credit.
In a system like ours (the world's that is - I'm not American) where money is created when banks write loans, debt increases more quickly than the money supply (because debt has interest, money doesn't, and in a housing boom relatively little new real value is being created). So the debt can never all be repayed, and at some point there must be a financial crisis.
Unless this time is different?