First, what's the Fed's argument for keeping this information secret? Bloomberg explains the Fed's reasoning given to the judge, Loretta Preska:
Preska's Aug. 24 ruling rejected the Fed's argument that the records should remain private because they are trade secrets and would scare customers into pulling their deposits.The trade secret argument seems a bit of a stretch. Are there really banks out there claiming that the secret to their success is getting loans from the Federal Reserve? That seems highly unlikely.
The other argument, however, is relevant and important. I see it as the crux of the Fed's case. Let's imagine your bank needed an emergency loan from the Federal Reserve. Currently, you'd never find out, since it's secret. But if the Fed ultimately loses the case, then imagine if its emergency loan balance listing by bank became published daily for public consumption. You could see your bank on there. That might, and probably should, cause some alarm to those banks' customers.
The Fed's argument is essentially that disclosing this information will cause bank panics. Ignorance is bliss. If people never find out about these loans, then assuming the bank pays it back, everything will turn out fine. Why scare the public for no reason?