Keep him. At least he's got an open mind and can think for himself.
It's unfortunate that the first person who seems to have noticed the vaccination-autism link, jumped to conclusions regarding causality, thereby messing up the debate. He also overstated the case of the Amish; they do get autism, just not at the rates we do. And some of them vaccinate, but others don't. It probably depends on their Ordnung (their community rules). They seem to have no objections to technology as long as someone else does the worldliness dirty work for them (they'll accept rides in your car if you are on friendly terms with them--they just won't own one and won't drive one), and so they are sometimes somewhat passive recipients of technology.
Their lower rates are probably the result of a combination of lower vaccination compliance (they tend to ignore "English" laws they don't feel have any relevance to them) and working outdoors more (higher levels of natural vitamin D).
