One of the characters in the classic 1939 film “Stagecoach” is a banker named Gatewood who lectures his captive audience on the evils of big government, especially bank regulation — “As if we bankers don’t know how to run our own banks!” he exclaims. As the film progresses, we learn that Gatewood is in fact skipping town with a satchel full of embezzled cash. As far as we know, Jamie Dimon, the chairman and C.E.O. of JPMorgan Chase, isn’t planning anything similar. He has, however, been fond of giving Gatewood-like speeches about how he and his colleagues know what they’re doing,…