Herd immunity is a thing. Knew a girl in high school who couldn't get vaccinated because of assorted medical reasons.
Parents like that not only endanger their own kids but kids like her. And that's not getting into the fact that vaccines aren't 100% effective so even my vaccinated kids could end up with measles if they have bad luck.
I know I'm preaching to the choir I just want to find that parent and punch her.