[autodidakto]

You have an insight (bankers are self-selected to be more greedy than average), but the author's point still stands: people underestimate their tendency to do bad things when offered enough money. He phrased it in a way that might seem to morally protect the bankers ("he who is not guilty of greed may throw the first stone..!"), but I don't think that he is trying to argue that the guilty shouldn't be punished.