We live near Amish communities in Michiana ... they do have children with birth defects and disabilities and let them stay in public school as long as possible for free help from the state.
My dad used to be a “Yoder toter” (van driver) and one of the saddest trips was to Riley Hospital in Indy where an Amish neighbor baby died of birth defects.
They love junk food as much as anybody else. The next time you are behind an Amish lady with a $500 grocery bill, sneak a peek ;-)
Not all the men farm or work in home workshops. A large number work in factories and smoke and drink as much or more than the English men.
Finally I had some relatives with Aspberger’s ... one born in 1925 and his mom said she had relatives from the old country who were “that way.” They would have been born in the 1800s. No vaccines. Maybe exposed to pollution?
No easy answers.
Main thing is their closed communities make it hard for them to get to Hardy-Weinberg equilibrium so they have lots of autosomal recessive things going on with their people.