An increase in the number of diagnoses vs. the number of cases that exist, is not really the point. We are really more concerned about why some kids are autistic--however many it may be.
There are so many things in our environment that have changed since the 70's, including the levels of estrogens, hormones, food colorings, and preservatives in the diet; the levels of use of electronics and filtered air in the home; the types of chemicals that are used to manufacture building materials, paints and carpets; chemicals that have been removed from the environment like lead in paint and pollution; personal health habits like the use of Advil and acetaminophen rather than aspirin; the increased use of birth control pills, latex condoms, latex gloves, factory-produced vitamins, insecticides; and there is an increase in the routine use of sonograms during pregnancy.
Any one of these things or something completely unrelated could be the culprit.
Keeping in mind that autism affects three times as many boys as girls, it would probably behoove researchers to explore the testosterone connection.
Well, I totally agree with you. I've always thought that in 50 years we'll look back at many of our common practices of today and say "what the hell were we thinking?"