You need to ask:
What makes an illness an illness?
What if someone likes the way they are?
What proves something is a mental illness versus merely labeled as a mental illness because society doesn't like it? And if it's for that reason why bother labeling it "mental illness" instead of criminalizing the conduct and offering up rehabilitation programs to reduce the chance of criminality and then offering parole for certain offenders.
As for "mental illness" based on personal distress rather than offending society why not just call it therapy for subjective distress and say there's nothing wrong with people who feel bad for what ever reason getting help in feeling better rather than using a complicated labeling system? Without calling it "mental illness" the FDA could still regulate what doctors can prescribe as treatment and under what circumstances.
If you try to use neurochemistry to "prove" mental illness then consider, In our materialistic universe every variation of thought or behavior is bound to have chemical correlations in the brain. So is every variation from "normal" an illness? How do we decide what is "normal"? What is that based on? Does society have an infallible right to deem what ever it wants as "mental illness"? Was drapetomania a real mental illness back when it was considered one? If not is there some objective standard we can use to determine when society is wrong?
I believe as a race, humanity loves to label things. They love to be able to point at someone and say, yes, this is what is wrong with you. I believe if everyone was assessed for mental illness, everyone would get some kind of diagnosis, so I do believe Dr. Thomas Szasz's body of would should be accepted and understood by psychiatrists. Just because you study theories doesn't mean you have to anihilate the whole subject however.
It's easy to see why psychiatrists resist Dr. Szasz's body of work. Essentially, in doing so, they're putting themselves out of work by agreeing that the conditions they're trained to treat are not legitimate. There is, however, evidence to support Dr. Szasz's claims. The simple fact that there has been a steady rise in conditions accepted as mental illnesses in recent years to include such common and inevitable human ranges of emotion as grief is one key example. Another supporting argument is the nearly complete lack of mental illness prior to the rise of the practice psychiatry.
Thomas Szasz's body of work was intriguing (yes, that's a nice way of saying controversial), to be sure, but it isn't considered credible by anyone these days. The idea that mental illness isn't real was designed simply to be contrarian and create dialog, and the consensus since his books on the subject were published in the 1970s, is that he was wrong.
No. Dr. Thomas Szasz was being contrarian simply for the sake of being contrarian. There's a small but vocal minority out there who don't like the fact that mental illness exists, because they have control freak tendencies. And there's nothing a control freak hates worse than being told they have an illness that cannot be fixed by pills alone. Szasz was a fraud.
Dr. Thomas Szasz's body of work should not be accepted by more psychiatrists. This would be the wrong course of action for any psychiatrist. Dr. Thomas Szasz's ideals are not proven and he does not know what he is talking about. I think a psychiatrist should continue to use their own methods.