I expect the grown-up would probably look confused, then question the child further. The well-rehearsed child would then explain the negative externalities that society has imposed upon itself by reducing these risks to near-zero, and how it is optimal for society to only reduce these risks until the marginal benefit of further risk reduction is equal to the marginal cost.
At this point, if your child has managed to make the case effectively, the grown-up would realise that the child is probably mature enough to make their own decisions whether to stay outside alone or not.
I expect the grown-up would probably look confused, then question the child further. The well-rehearsed child would then explain the negative externalities that society has imposed upon itself by reducing these risks to near-zero, and how it is optimal for society to only reduce these risks until the marginal benefit of further risk reduction is equal to the marginal cost.
At this point, if your child has managed to make the case effectively, the grown-up would realise that the child is probably mature enough to make their own decisions whether to stay outside alone or not.