I am not sure how to tackle you questions. You seem to be talking about clinical psychology, which unfortunately (as you outlined below) has been prone to fads and unethical (by today’s standards) behaviour by clinicians. I think you will find that most legitimate therapy is evidenced-based. However, it is important to get a proper diagnosis as therapy has limits.
I am not really that interested in clinical psychology and am more interested in how the brain works from a biological to sociological perspective, e.g. the social impairements of autism are believed to be due to the impairement of something called the theory of mind (possibly the amygdila-sp?), i.e. an empathic understanding of someone elses thoughts and feelings through the reading of verbal and non-verbal cues. This can be tested by seeing if people with autism can work out what someone else is thinking and feelings. The more severely autistic an individual is the less well they do at these tasks. I pass all these tasks about the same as the average population but worse then an equivalent non-autistic person of my IQ.