It's not just that a genetic cause for autism would be repugnant to many, it's that the vaccination hypothesis is clear and simple. There is an appeal to a simple explanation, because a simple explanation holds the promise of prevention, treatment, and/or cure.

It's possible that there is a heavy metal/genetic predisposition link in autism, but I'm not going to go out on a limb and say it's probable. Like most neurological and neurochemical phenomena, autism probably is the result of many interactions with many critical control points. And, I suspect, that this makes even a heavy metal hypothesis not the only valid hypothesis or the only possible cause of autism.

Finally, with the very broad spectrum of disorders which are classified as Autism spectrum disorders, I wonder if the disorder has been made too broad. There are fully functional people at one end of the spectrum, even if normal people might call them "odd ducks", "highly talented", or "eccentric", and at the other end are severely developmentally disabled individuals who might also not properly belong in the Autism spectrum.