Last September 11 a writer not much older than myself worried that, as more and more people too young to remember the terrorist attacks of 2001 aged into adulthood, the date might lose some of its emotional charge and political significance. I fall comfortably into the age group in question here: I turned two a few months before that fateful day, and my first memories all come from years later. The events of the early aughts, from the toppling of the Twin Towers to the invasion of Iraq and beyond, exist to me only as history. I’m not sure that’s a bad thing.
Much has been made, year after year, of the unity that seized America in the wake of the attacks, and not without cause. Remarkable acts of heroism, not to mention ones of kindness, defined the immediate reaction that September. We...