If you believe that way too many people with high credit risks have too much access to credit, which they then use to make a mess of their lives, and that it’s a legitimate role of government to protect them from themselves, then the cost–benefit analysis of capping credit card interest rates looks different from the one most of my colleagues have outlined. The cost of fewer credit card offerings to the marginal consumer becomes, to a large degree, a benefit; and that benefit helps offset such undoubted costs as the curtailing of credit card rewards and other perks.
But I don’t think that even the paternalistic case nets out in favor of the proposal. How many of the people denied credit cards (or effectively denied them, or limited in their credit lines) would turn to worse sources of credit? Presumably nobody wants to pass a Full Employment for Loan Sharks Act (except for the loan sharks).