Mental disorder seems to often be informally defined as any behaviour or opinions that are sufficiently distant from what is considered normal. This means that in one culture, a behaviour could be mental illness while in another it could be normal.
I have previously commented on cultural interpretations of insanity. Barracking for the wrong sports team, the wrong political party, the wrong singer or actor ... signs of psychosis? There is a long history of the nature of mental illness being questioned, from both within and outside of psychiatry. Its not been long since there was essentially a homophobia promoted diagnosis, and there was serious efforts to make more than normal PMS a psychiatric condition.
In history people were incarcerated in insane asylums for diabetes and multiple sclerosis. MS was considered a mental disorder in my lifetime ... and some psychs still make that claim, as recently as last year.
If you read contemporary (last several decades) accounts of how psych disorders are created and defended, its horrifying. Like two psychs on a boat on a fishing trip coming up with a new diagnosis. How these diagnoses are validated also has not much to do with the existence of the proposed disorder.
Theories that mental diseases were due to germs, early last century, led to surgical removal of all teeth or colons. Other atrocities abound, and most were probably not recorded in a way we can easily find out about.
We like to think times have changed, medical professionals like to claim times have changed, yet still people with ME and other complex diseases get held against their will, for unproven treatments for unprovable conditions, and some of these are children.
One of the big issues that needs addressing is how the global medical profession tends to remain silent when these things are happening. Some do speak out, but its a rare exception and not the norm.
One of the factors pushing this seems to be the promise of cheap and easy solutions. To those politicians and bureaucrats, please come forward and we can tell you about the miraculous properties of snake oil.
Psychiatry does need to create a sound scientific basis. To do so the standards of quality science cannot be relaxed. I wish the authors of the PACE study knew that.