Jonathan Alpert has been a psychotherapist for decades, but in his new book, he questions whether his profession is doing some people more harm than good. “Therapy has never been more ubiquitous, yet we’re anxious, fragile, lost, and more divided than ever,” he writes in the introduction to “Therapy Nation: How America Got Hooked on Therapy and Why It’s Left Us More Anxious and Divided” (Hanover Square Press).