No doubt you are aware of the flap over vaccination triggered by an outbreak of Measles in California. Apparently, lots of up-scale tree-hugging eco-friendly Whole Foods types have chosen not to have their children vaccinated. [I pre-emptively apologize for the deliberately offensive language.] It is thought that the outbreak started at DisneyLand.
Why shouldn't parents have the right to choose not to have their children vaccinated? Because that choice puts at risk the children who have been vaccinated? How on earth could it do that? Because the vaccine is only about 97% effective. Communicable diseases need an accessible pool of target organisms in order to spread. Otherwise, even though the bacterium or virus is live, it fails to come in contact with an organism it can infect. Even if it does find one, that one is unlikely to encounter another. With 97% of potential targets ruled out, the odds are just too small for an epidemic.
Enter a bunch of kids whose parents have decided not to have them vaccinated. Their presence significantly increases the probability that an unsuccessfully vaccinated child will be infected. So parents who claim to be exercising a parental right are in fact willfully endangering the children of other parents, and that they have no right to do.
I freely confess that I did not fully understand this until I came across a story somewhere that made reference to it in passing. This is hardly rocket science or brain surgery, but it is apparently beyond the grasp of politicians and television commentators.