Millennials are not some vast unsolvable mystery. According to a report from the U.S. Census Bureau (PDF), they earn $2,000 less than their parents did at a comparable age, they are more likely to live in poverty, and they are more likely to live at home. But Baby Boomers and Gen Xers still seem to find it hard to believe that basic economic math can explain much of the younger generation’s behavior. After several news outlets, including The Daily Beast, reported that rates of millennial sexual inactivity in early adulthood are surprisingly high, armchair social theorists came out in force...