Szasz burst on the scene nearly 60 years ago with his pathbreaking book, The Myth of Mental Illness, which argued that the mind, not being an organ, cannot be diseased; thus the term "mental illness" is a category mistake. What is stigmatized by that "diagnosis" is the "patient's" behavior that disturbs someone else. The switch from "mental illness" to "brain disorder" did not change the fact that what is typically bothersome is behavior (which may indeed be objectionable and even coercive). The attribution of such behavior to a brain state is an unproven and even unprovable inference. Human action has reasons, not causes, Szasz would say.
At Amazon.com you'll find a cornucopia of books demolishing the case for the state's deputization of physicians, particularly psychiatrists. A good book to start with is Insanity: The Idea and Its Consequences, his magnum opus. You should also search his name at FEE.org for the columns he wrote while I edited The Freeman.
Meanwhile, to get a sense of what Szasz was about at the deepest level, see my "Szasz in One Lesson" and watch this interview I did with him.