The experience shook me, largely because of how angry I found myself becoming. Some of that anger was because of the implied challenge to my knowledge (well, gee, I've only been reading studies for 30 years) but a large chunk of it was what I can most accurately describe as parental rage. Part of me wanted to say "You may not know it, but you want my son to be dead, and that is not OK." C's prematurity meant that he had a completely screwed-up immune system (not to mention lung damage) as a toddler; he's exactly the kind of kid who would be expected to die in an outbreak of any of the standard preventable childhood diseases. I care somewhat when people are misguided enough to put their own kids at risk, but way more when they're putting mine at risk too.
And that was even before I got (in my esprit d'escalier while cruising the vegetable department) into the part about anti-vaxers being a bunch of irresponsible freeloaders who get to take advantage of everyone else's socially-minded behavior while avoiding any perceived risks for themselves. This is something that just pisses me off.
I don't know. Maybe I should have handled things differently. Just politely accepted a leaflet and moved on. Or said "no thanks". Or said, "Why would anyone possibly want to pass up a chance to protect their child's life and the lives of other children?" or "You know that the whole autism thing was started by a guy who was paid to fabricate data by an ambulance-chasing law firm, don't you?"