Having "good credit" would imply doing something like having paid off six figures in student loans or the mortgage on a house, which requires paying many thousands of dollars in interest, so that credit history would have a high market value and defaulting on a loan taken against it would destroy that value. So that system would work fine -- it might cost the bank money to go through the inconvenience of foreclosing on a house, but it would cost you just as much for the good credit you destroyed in doing it, so it's symmetric and people would have an adequate disincentive to do that.