I am with HK on this one. And I have had parallel experiences--though I am in the social "sciences", and I am a believer. (Although my background in the hard sciences has probably led to very similar conversations with anti-vaxxers in particular.)
The thing is, people--all people--have some beliefs which they hold for no rational reason, or emotional responses which are not logical. It is ineffective to try to challenge those beliefs or responses on purely rational bases (though there is absolutely a time and a place for presenting the facts and the logic--but not when they are being flooded by feelings, when they won't be able to hear it anyway). Since the belief or response arises from a social-emotional origin, it can really only be addressed using a social-emotional approach, that acknowledges the authentic feelings generated, and the relationships involved. (On another topic altogether, this is why there is widespread support for many school safety initiatives, despite the facts--which are that your kid has a much higher chance of dying in a car accident than in a school shooting. But it makes adults feel like they are doing anything they can to protect vulnerable children to have locked-down schools, weapon-carrying security personnel, etc.)
In addition, an individual's motivation for behaving in a specific, non-rational way is often complex. Unless you have access to their motivations, it is unwise (and often inaccurate) to make assumptions about their motivations. And even when motivations are voiced, they are sometimes incomplete, or even misread by the individual themselves. Especially when you are talking about very young children.
Whether or not you are normative, it is well to learn to understand that there are certain principles and values which are worth confronting the norm of the group in front of you right now, and many other moments for which quietly letting the group swirl past you is essentially harmless to the group, and beneficial to the relationship. This does not mean having to pretend to be afraid of a harmless arachnid, nor does it mandate condescending to others' fears. There is a significant continuum in-between, which most of us are in an ongoing process of negotiating...
