There’s nothing wrong with alternative, testable hypotheses in science.
But the autism-vaccine link hypothesis has been pretty thoroughly tested and disproven. Autism is caused by a combination of genetic factors and environmental triggers. Mercury exposure *can* trigger autism in some individuals, but this is they type of mercury pumped out by industrial smokestacks, not the type found in vaccines.
Autism is especially tricky because it’s strictly behavioral in terms of diagnosis (at this time) and it truly is a spectrum disorder. Some autistic individuals don’t even like it being considered a disorder at all, any more than being shy or liking adrenaline rush sports are considered disorders.
Fortunately we understand Autism now far better than we did a decade ago, and are making more progress every day. Better real answers do help avoid the public at large trying to fill in the blank with anecdotal conjecture.