First off I'm pro-vaccination. However this example doesn't really add up for me. I'm not a doctor, but if the rest of us vaccinate our kids, won't they NOT GET SICK? Hence calling it an immunization.
So if the rest of us are immunized the only people getting sick are the anti-vaxxers. For this allegory of the Car Brakes and Social Responsibility to truly be a 1-to-1 comparison of social risk with regards to pro/anti immunization he'd have to basically present the premise that everyone else who has car brakes is protected from the less informed anti-brakers.