Some know little and believe a lot, others know more but do not believe in much. Some I suppose believe a lot and also know a lot.
Severe mental illness is the result of organic disease or genetic and environmental factors. This is becoming increasingly clear from magnetic resonance studies apart from any other evidence.
The fact that drugs can assist is also evidence enough. Ask my neighbor Dennis if he'd care to go off his medication for schizophrenia. I doubt he wants the symptoms back. The fact that he can now hold a normal conversation and a part-time job probably seems better to him than cowering in some hole terrified of visions and voices in his head.
No! Have you ever been to a psych hospital? If not, then I suggest you take a visit. You will not think mental illness is a conspiracy theory any longer.
Have you or anyone you ever loved suffered from a mental illness? I think if you had more experience with it you wouldn't pose such an obviously stupid question. Is suicide a conspiracy theory? Is self harm just some massive 'in joke' that you don't know about? I think not. Maybe a little bit of scientific research or volunteering to help people with mental illness would give a more subjective view.
Any lie you tell yourself long enough, you will believe it and it will be your truth. You will even be able to pass a lie detector test about it.
What is your definition of mental illness?
If you accept clinical diagnnoses as legitimately identifying abberant and abnormal behavior resulting from brain dysfunction, then you believe in the existence of mental illness, by definition.
The only way conspiracy theory could come into the discussion is if you simply don't believe in the existence of brain dysfunctions that result in abberant or abnormal behavior.
I would submit that there is overwhelming evidence that such behavior exists, and I am willing to accept brain dysfunction as the cause of most of it.
Who would you be pointing the finger at as the co-conspirators?