Mother Jones has just run a very nice analysis of recent years' research on state laws governing non-medical exemption from childhood vaccines. It turns out that if a state makes it very easy for parents to exempt their children from recommended school vaccinations for non-medical reasons, lots of parents will exempt their children. This causes loss of herd immunity, and children die of childhood diseases that haven't been common for decades. And when one state (Washington) tightened up its rules by requiring a doctor's signature for exempting children from vaccination, exemption rates fell by 40%.
Meanwhile, cases of measles are on the rise in California--more than half of them involving children who were intentionally not vaccinated.