Despite its longstanding interest in the problem of money (beginning with getting more of it), Economic Principals has been reluctant to turn to coverage of banking because it’s essentially a full-time, boring job, for writer and reader alike, and we seek to cast a pretty wide net. A Wall Street Journal series last week indicated the scope of the problem. “What Is A Bank?” featured eight stories over four days by eleven reporters on three continents, beginning with “The Existential Crisis That’s Stalking Banks.” Sample fact: The mighty Goldman Sachs in the last twelve months delivered a return on equity…