There are big, complex problems over on Wall Street, but ultimately they boil down to one problem: if someone is greedy enough, no law, regulation, or humanity will stop them from grabbing whatever money they can. Hence the easy solution:
Add a one-question test, with a lie detector, as a requirement to do any work in the financial industry.
"Is Gordon Gekko the hero of the 1987 film Wall Street?"
If they answer yes, they fail forever. If they have no answer, they have six months to watch it at least five times, along with a minimum of one viewing of Bambi, and retake the test.