I don't believe that there is an all or nothing answer. I think it must be partially genetics in our case, as my dad and FIL were/are both fairly aspie, and the women tend to have autoimmune problems (anyone read about the rubella vaccine and women who don't retain immunity? That's us)
However, something had to have pushed my kids from slightly aspie to full-blown autism, and I do believe vaccines had something to do with it. I am blessed (I guess) in that my oldest two DID have severe reactions, so it's not a theory...seizures, 108º fevers and immediate regression within days of vax are pretty obvious. I also have the benefit of having a large family (control group) of kids who have not been vaccinated. DH and I have five younger children who have not been vaccinated, and who are quirky but not full-blown like the older two. We also have a large extended family on dh's side, (36 first cousins, none vaccinated) some of whom are quirky but not one who is autistic. If it was genetic, the odds of having so many children NOT affected, is unbelievable.
Oh, and I really don't believe in the whole silicon valley theory...working as an advocate in the schools I've met too many parents who were not genius and had children with autism. Sorry, mean sounding but true.