Question - Why does Tom Cruise hate psychiatry?
Answer - Because he is a Scientologist.
Tom Cruise recently did an interview with Matt Lauer in which Cruise chastised Lauer for defending the discipline of psychiatry and Cruise has generally been a fairly vocal critic of the use of medication to treat mental disorder. The root of Cruise's distaste for psychiatry can be traced to his Scientology beliefs, since scientology itself is a form of psychological quackery.
Martin Gardner, the father of the modern skeptical movement, explained and debunked Dianetics, the psychology of Scientology, over half a century ago in his seminal text Fads and Fallacies in the Name of Science. Despite Scientology's sci-fi origins and dubious and potentially dangerous psuedo-therapies, there are people such as Cruise who still become believers.