The decision's release on Charles Darwin's 200th birthday was fortuitous, the "vax/aut" crowd having not a little in common with the fundamentalists who so despise the father of evolutionary biology. Like fundamentalists, vax/aut proponents have become so invested in the truth of their particular idea that they ignore, rationalize, or attack as fraudulent any evidence to the contrary. Evidence in favor of their idea is distorted and endlessly repeated, and gaps in the evidence for alternative ideas are treated as further proof.
I suspect that fundamentalists' ire for Darwin goes beyond evolution, and stems as much from the approach to knowledge for which he stands. Setting out on the Beagle, Darwin held an idea common among 19th century Anglicans: that modern plants and animals descend from nearly identical ancestors created by God at the beginning of the world. But when Darwin's observations in the Galápagos suggested an alternative hypothesis, one that better fit the newly available evidence, he abandoned the old idea. This methodology for approaching ideas--evaluating them for explanatory success and then refining or discarding them in light of new facts--poses an existential threat to the entire project of fundamentalism.
The genesis of the vax/aut hypothesis was not in itself irrational. Certain forms of autism tend to manifest around the age at which most children receive MMR. And mercury, an ingredient in the vaccine preservative thimerosal, is known to cause neurological damage in vastly larger quantities.
But subsequent analysis has revealed the conclusions drawn from timing of onset to represent a simple post hoc fallacy. The incidence of autism turns out to be the same among children receiving vaccines with and without thimerosal, or receiving no vaccinations at all. And here is where the vax/aut enthusiasts show their fundamentalist stripes. Like the contrarians who insist the moon landing was faked and Snapple is sterilizing African-Americans, vax/aut types are unmoved by the evidence.
It's not that vax/aut believers aren't sympathetic--many are parents of autistic children and understandably yearn for any explanation of the otherwise inexplicable devastation wrought upon their families. Often they have been seduced by cure-peddling quacks and book-hawking celebrities.
But the vax/aut faithful provide red meat to the "anti-vax" movement: parents who refuse to vaccinate their children and think you shouldn't either. The obscenity of this movement's attack on perhaps the greatest public health achievement in history is stupefying. A campaign to reinstitute open sewers or ban refrigeration could scarcely threaten greater violence to the general well-being.
Tragically, anti-vaxers may be validating Darwin as we speak. More than survival or even reproduction, the traits most favored by natural selection are those that ensure an organism's offspring survive to reproduce. If credulity is a heritable trait, forgoing vaccination is an excellent way to boost the odds your children won't pass it on.