Autism is neurological damage. So, there is not one cause of autism. There are many. Vaccines can be one of them. Pesticides can be another. I think asking what is THE cause of autism rather misses the point. It’s like asking what is the cause of bleeding. Obviously, if you stick a knife into your gut, you’ll bleed. If you shoot yourself in the head, you’ll tend to bleed. If you fall off your skateboard and scrape your knee, you may bleed. Same principle with autism. If you do something that damages your brain (… you know, like inject yourself with mercury, aluminum, formaldehyde, etc.), you may well develop symptoms of autism or other related disorders.
Autism is kind of like bleeding