Science and Psychology
You need to keep in mind a very important aspect of diagnosing “mental diseases”: they are ALL diagnosed using ONLY observation of behaviour. There is no way for a psychologist to look at someone´s brain and tell if he or she has schizophrenia, anxiety, is depressed or has any other “mental disease”.
From Wikipedia: “A mental disorder or psychiatric disorder is a psychological pattern or anomaly, potentially reflected in behavior, that is generally associated with distress or disability, and which is not considered part of normal development in a person's culture. “ Psychologists have a book called DSM (Diagnostic and Statistical Manual of Mental Disorders) that contains definitions of various “mental illnesses” and most if not all of them are VOTED on to be included in the manual.
Allen Frances (Chair of the DSM-IV task force) concerning the new DSM-V:
“In June 2009, Allen Frances issued strongly worded criticisms of the processes leading to DSM-5 and the risk of "serious, subtle, (…) ubiquitous" and "dangerous" unintended consequences, such as new "false 'epidemics'". He writes that "the work on DSM-V has displayed the most unhappy combination of soaring ambition and weak methodology" and he is concerned about the task force's "inexplicably closed and secretive process.".You can see this 2015 lecture by Allen Frances describing in detail his critique about diagnosing people with 'mental disorders'.
When a medical researcher wants to identify a new illness, he or she acquires images of the responsible pathogen, discovers its vulnerabilities, creates a treatment that's vetted in clinical trials, and then publishes his or her findings. That's how modern medical practice is managed. When a psychologist wants to identify a new illness, he gets together with like-minded psychologists, they hold a secret meeting and they vote. That's how psychology is managed. And this alone makes such diagnoses unscientific, to say the least.