Yeah, they will respond: They will slash credit lines; they will triple the fees; they will increase transaction fees; and they will deny credit to marginal customers.
You cannot expect the stocks to rise continually and at the same time put in price controls.
Price controls NEVER work.
Funny thing is, I have top a tier credit rating and I am sure the rates I pay factor in their losses from marginal customers... Credit should earned, not given away. Of course then the banks will accused of discrimination.