There are no mental illnesses, only popular viewpoints and behaviours, unpopular viewpoints and behaviours (what people call mental illness) and lastly actual damage to the physical brain.
Christians/muslims/jews believe there is a magical skydaddy that will judge them for an endless amount of contradictory viewpoints that are impossible to follow in the bible, both extremely good and evil (subjectively)
In indigenous north america and ancient china, they believe the world is a giant turtle.
Pagans (norse) believe it’s the body of yimir (greek) the body of the primordial titan Gaia.
Scientologists believe it’s Overlord Xenu! ruled a “Galactic Confederacy” of 76 planets, including Earth (called “Teegeeack”). The confederacy was supposedly overpopulated, so Xenu supposedly had billions of beings frozen and brought to Earth in spacecraft resembling DC-8 airplanes.
All of these philosophies, are considered totally logical, rational, sane healthy and correct despite having no physical evidence.
To believers of the other, are considered wrong, and the scientology one is considered mental illness by all the rest, why? Because it’s not POPULAR, might makes right.
The only true mental illness is literal damage to the brain.
There are no mental illnesses, only those arrogant enough to consider those who think or behave differently than them sick.