Indeed. If you want talk to them with their terms, you might have better luck with "God helps those who help themselves", though I doubt that will work in practice either.

Sure, but it's not like they're consistently anti-medicine, happily 'helping themselves' to cancer treatments and the rest (well, except for the oddly named Christian Science sect, but not the broader Bachmann-style evangelicals that are found overlapping with the anti-vaccine movement these days). It's almost like existing biases helped them succumb to the original fraud and helped them get stuck in it, so now they just truly believe that most medicine helps but vaccines cause autism. Fortunately it doesn't seem to be spreading across evangelicals as a whole.