Autism is a scary disease for parents. Consider the cycle of life, at least from a psychosocial perspective. Parents want to see their children grow up, get married and have a successful career. They probably want grandchildren too at some point. Autism can stop all of that. So people look for causes. Mercury in the water supply and in some of the foods gleaned from water (fish and mussels) have been known to have high concentrations of mercury. It is possible that this is one culprit. Unfortunately, though it is known that autism can be caused by many things, no one cause is known.
I have a feeling that it is one thing in a long list of possibilities. But who knows, it could just be general makeup in our DNA that causes someone to be born with autism or anything similar to it. Or, shall I say, chemical makeup of the brain.