Ten years ago, after making piles of money gambling with other people’s money, Wall Street nearly imploded, and the outgoing George W. Bush and incoming Obama administrations bailed out the bankers. America should have learned three big lessons from the crisis. We didn’t, to our continuing peril. First unlearned lesson: Banking is a risky business with huge upsides for the few who gamble in it, but bigger downsides for the public when those bets go bad. Which means that safeguards are necessary. The safeguards created after Wall Street’s 1929 crash worked for over four decades. They made banking boring. But starting in the 1980s, they were watered down or repealed because of Wall Street’s increasing thirst for profits and its growing political clout. As politicians from both parties grew dependent on the Street for campaign funding, the rush to deregulate turned into a stampede. It began in 1982 when Congress and the Reagan administration deregulated savings...