GS didn't try to regulate investment banking risks. It sheltered commercial banks from them. The rise of "shadow banks" via money market funds kills that approach. Commercial bank deposits would flow to money markets, who would give higher, unregulated yields by funding commercial paper of investment banks and structured product vehicles.

You could try to regulate the money funds, but now you're trying to regulate investment banking risk, something GS never really tried in the first place.

There are no "old days" for this financial structure, the configuration of the size / public ownership / complexity / funding environment of these institutions is entirely new.