There's a few points I would like to make
(1) How is this different from any other subject of film (or drama, novels, etc. ) ? Think "Mr Smith Goes to Washington" vs "House of Cards" or "The Guns of Navrone" vs "Inglorious Basterds". There was more of a habit of hushing up bad things in those days, so in some ways we're more honest now than we were then.
(2) the way things were fifty years ago was not half as rosy as the author would like us to make it out to be. These were the days of the Macarthur hearings, Jim Crow laws, coverups about harmful pesticides and tobacco, and numerous other unethical behavior that have caused greater harm to people.
(3) Shady stock operators were around then too. Probably just as many, and they worked the same way on exploiting people's hope, greed, and ignorance. The difference was that they couldn't scale up the way that they could thanks to technology making it easier to have one of them get bulk quantities of victims.
(4) As globalization happens, the industry and the economy in general become much more brutally competitive. People sometimes feel they have to cut corners to make things work. This is a point where the CFA Institute has made a contribution, by showing there is a way to thrive while treating people correctly and giving an imprimatur that helps assure the public.
(5) It's a lot easier to act unethically towards someone who is an abstraction rather than a face in front of you (that didn't prevent that many people, see (3), but still). Again, communications technology becoming cheaper and more prevalent has played a role.
(6) Trauma and threats help bring a community together out of fear of an other. In the 50's we had bulk quantities of nuclear-armed Soviet bombers, threat of a major war in Europe, the trauma of WW2, etc. We're better off not having those (and despite some politicians' attempts to claim it, terrorism has not been an existential threat on anywhere near that scale), but they did bring an "us" vs. "them" mentality that made it harder to rip off one of "us"