Of course the chemicals we live with are another potential explanation. The job, though, of the medical research community is to do wide-ranging double-blind studies and find out.
From everything I’ve seen, the anti-vaccine people are the ones saying this is a hypothesis that should be studied, while some of the folks on the other side are the ones saying that further research on the link would be “counterproductive.” There goes the scientific method out the window.
Do the study. If there’s no link, fine, we’ll find that out.
BEcause the benefit of the vaccines probably do outweigh the benefits in general, but it sucks to get the short straw and have your child turn up autistic at age 3 after being an extremely bright child up to that point, then reversing.