Karen: "WE GOTTA GET RID OF GENETICS!"

My guess would be that, if autism is being diagnosed at an exponentially increasing rate (as you are suggesting), it is because our world has seen a dramatic increase in the number of teratogens, such as pollution, carcinogens (especially in our increasingly processed foods), etc. Another factor may simply be that doctors have become more sensitive to the disorder, thus it is being diagnosed more often.

To clarify that last point. It has only recently been recognized that autism is a spectrum disorder. Therefore, in the past, people who may have simply been thought of as geeks or otherwise antisocial are more commonly being labeled as part of the autism spectrum.