I think they’re coming from a painful place, Sherry, at least for this cycle of vaccination fears.

There is something wrong with my kid, and it must be somebody’s fault… and not mine!

— seems to be how things got started, with autism fears.

It’s too late for my kid, but I can save others. My child shall not have suffered in vain!

Who are you (or anyone) to tell them that their child is a victim of a statistical fluke?

Numbers… who cares about numbers? This is a child’s life we’re talking about!

And then (as others have pointed out) you throw in the medical profession’s well-earned reputation for not listening to the pains and concerns of women, despite evidence, and a certain amount of “the guvmint can’t tell me what to do!”, and it all goes downhill from there. <sigh>