 Plato was horrified by a newfangled thing called writing. The town fathers of London were horrified by Shakespeare. And archbishops in America were horrified by the birth of swing music. So in England, in February of this year, two mothers were talking at the school gate after they dropped off their 11-year-old kids. Both of them were alarmed by the number of 11-year-olds owning smartphones and by the sort of research on childhood anxiety and depression that had disturbed Jonathan Haidt.