I don’t think mercury helped (my son was vaccinated in the “mercury” days), but I do think the amount of vaccines given sets off some sort of auto-immunity problems. I think it’s also a reason we see so many food allergies. Didn’t know a single kid with peanut allergies as a kid in the 70’s and 80’s, and now there are at least a few in every school, and I do think these are valid allergies (some on FR consider it to be over-protective parents, over-pampered kids.)
We really don’t know other than make observations and educated guesses. Experimentation is the key to narrowing the factors. Like I said earlier, studies on the Amish, who tend to stay in one place and not mobile like modern families have an autism rate 1/100 of average Americans, while attempts to study mobile modern families are harder to control. Thus the observations of Amish population gives us an opportunity and maybe clues to what may cause autism. What is needed is a good control experiment (ie modified immunization schedule) to see if there are any effects on autism rates. So far no state is willing to do such an experiment.