Classifying: weak science or strong science?

On page W8 of today's WSJ was a book review so entertaining I have to quote from it. Reviewed by Paul McHugh, the book's title is "Shyness: How Normal Behavior Became a Sickness" by Christopher Lane. The gist: apparently some psychologists are causing an over-diagnosis of mental disorders that are really just personality quirks - physiognomy, anyone? Some quotes (emphasis mine, as usual):

• "These days, almost any restless and active boy, especially if he attends a school that has cut back on recess, runs the risk of being labeled as suffering from Attention Deficit Hyperactivity Disorder (ADHD). A military hero might well be assessed as having Post-Traumatic Stress Disorder (PTSD) if he shows any unease after battle. And it seems that no one can be sad in our time without being prescribed a pill for major depression rather than given consolation."
• "Field guides work for identification purposes, and when nothing better is available they stand in for a diagnostic tool resting on more essential distinguishing characteristics. But just as the field guides of naturalists can lead to a mixing up and confusion of species and varieties that look similar (as many "birders" will attest), the field-guide method in psychiatry has now, as Mr. Lane notes, often mixed up truly ill folks with shy, restless, sad and worried people -- in other words, just about everyone at one time or another."
• Although McHugh does not criticize the subject matter entirely, he insists that "the truth is that scientific investigations into brain mechanisms, behavioral controls, vulnerabilities of temperament and responses to life-adversities will gradually solve the problems he has identified. A return to either the master from Vienna himself or the mannerists who followed after him will paralyze the effort."

This is partly why I've put off the required psychology class so long--I'm a mathematician at heart and therefore prefer precise, not-overdone answers to questions and problems.