You're conflating global/local norms, which is the whole point. They are different. If I talk to a random American, I can safely assume they do not typically be

You're conflating global/local norms, which is the whole point. They are different. If I talk to a random American, I can safely assume they do not typically believe stoning people is a proper punishment for adultery, and even for the few Americans who do think that's reasonable, they also understand that's a fringe view. So the curiosity is when people hold fringe views that they begin to think are normal.