If you haven’t seen The Big Short, you should. The acting is superb and the story enlightening: a few brilliant outcasts each discover just how big the holes are that eventually bury the U.S. financial system in the crisis of 2007-2009. If you’re like most people we know, you’ll walk away delighted by the movie and disturbed by the reality it captures. [Full disclosure: one of us joined a panel organized by the film’s economic consultant to view and discuss it with the director.]

But we're not film critics, The movie—along with some misleading criticism—prompts us to clarify what we view as the prime causes of the financial crisis. The financial corruption depicted in the movie is deeply troubling (we've written about fraud and conflicts of interest in finance here and here). But what made the U.S. financial system so fragile a decade ago, and what made the crisis so deep, were practices that were completely legal. The scandal is that we still haven't addressed these properly....