One of the biggest changes in the banking industry after the Great Depression was the separation of commercial and investment banking. It took the form of the Glass-Steagall Act, which went into effect in 1933. Glass-Steagall led to the separation of JPMorgan Chase (JPM) and Morgan Stanley (MS), but thanks to the effective repeal of Glass- Steagall in 1999, investment and commercial banking are now back together.
It may be worthwhile separating them again. After all, would you trust a bank that's owed money by a corporate borrower to underwrite honestly that companies' common shares? Banks that do this would be in economic conflict with the people buying the shares. That's because the reason a bank would make the secondary offering would be to raise cash to pay off the money that the company owes the bank.