The big problem with a lot of mental disorders, whether they are neurological, chemical, hormonal, or simply behavioral is that we simply take the behaviors and responses people make and call it a disorder. Unless there is a big tumor or other rather obvious physical defect, there's still not much we understand about the brain. What we call Autism COULD be a single disorder, or it could be 50 or 100 different disorders each with a different cause and treatment. Remember when formal medicine was as old as psychology/psychiatry is now, people were still talking about humors. Our modern mental health knowledge is almost certainly almost as wrong. That's not to say it's bunk, only that we're sill learning, and have a long way to go. Even back in the days of humors, what medicine did was generally a little better than nothing, and the knowledge that was learned has led to our current medical advances.