The reaction was typically American, I believe was the suggestion. There are perverts everywhere, but people not subject to American levels of fearmongering don't typically visualise child rape and reach for a weapon when another human smiles at their child.
Well there was a gender thing implicit in my comment and I feel I have witnessed it across cultures. Unfortunately in this case I think for a lot of women the defensiveness is shaped by real experiences.
On the other hand if you remove the question of gender I would have to admit that many in the US are more guarded with strangers than people tend to be in other places I've been.