"If consumers mattered, your bank would offer one retail product. It would be part checking account and part credit card. And by that I mean your balance could either be above zero or below zero at any given point. When your balance is below zero, you pay interest to the bank. When it is above zero, the bank pays you interest. You'd have one plastic card that does what your ATM and your credit card does now.
If you needed more credit, you could secure your account with your home equity. That way you wouldn't have multiple types of credit with the same bank, where the bank hopes you misplace at least one of their bills so they get the late fee."