The issue is one of trust. It's safe for vaccinated people to go around without masks, but not safe for unvaccinated people, particularly including children too young to be vaccinated. I can't speak for others, but I've seen so much refusal to wear masks here before the vaccine was widely available that I do NOT trust that Joe Q Public going around maskless is actually fully vaccinated and therefore not a risk to my kid. And yes, my kid will still be wearing a mask, but that only provides SOME protection. Masking by all provides a lot more. And lets face it, kid mask compliance isn't perfect, they're little kids.