In the 90's the diagnostic rates in autism was 3 in every 10,000 children. It has not increased to 6 in 1000. That is so, so much higher.
Many very normal and healthy children are being needlessly diagnosed to get academic support and also because parents want something to blame other than themselves for their children problems.
Those who have true Autism are being negatively affected by the over diagnosis.
There have been some recent controversial opinion pieces that autism is being overdiagnosed, especially in the young. It's argued children are "outgrowing" the diagnosis, and if that's true, then they didn't have it in the first place. Others argue that it's becoming more prevalent. Personally, I think it's too soon to know if it's being overdiagnosed since researchers are only beginning to learn about autism, but it does sound like Asperger’s, which is on the highest functioning end of the spectrum, may be being overdiagnosed.
I think that because we still are unsure of many aspects of Autism that doctors are still unclear on how exactly to identify people who have it so they are over-diagnosing people with it, I think over time as our detection methods get better then we will be able to reduce the amount of bad diagnoses.
What people don't seem to understand is that autism is wider ranging than we originally realized. There is a wide range on the autism spectrum, from aspergers to down syndrome. That is a big reason why diagnoses are at higher number than they used to be. It's important that people are aware of this.
No, I do not think autism is being over-diagnosed. It is absolutely essential that children with autism receive care as young as possible. Unless a person has lived with an autistic child, it is impossible to convey the pain and despair a family goes through. I believe autism is increasing and we need to continue to diagnose it as early as possible.
While the ratio of diagnoses are going up, I believe that this is because more people are realizing that there is more than the simple "classic" autism case; nonverbal and unable to function by themselves. They are realizing that there are people who are higher functioning. I have an I.Q. Above 160 (Einstein level), but I have problems every day. The only difference is that I can talk and learn how to take care of myself. That doesn't mean I don't have autism.
Children with markers of autism who are not provided with the social-emotional-developmental support they need are likely to slip through the cracks of the educational system. It does not matter what the rate of diagnosis is so long as we get these kids the support they need so that they can grow up with greater potential to succeed.