While that exists, it also happens that people are under diagnosed for somewhat rare conditions. If you don't know you have a condition it cannot be treated. If you have an explained symptom that your doctor can't explain and suddenly you find an explanation it is correct to see the doctor who understands it enough to diagnose you.

Of course the above gives quack a start, once you can explain something with BS you can spread it for money. I don't have a solution.