They know better than highly intelligent scientists, evolutionists, biologists, and geneticists JUST how sex works. It's hilarious.
And also better than parents.... there's a good reason why MumsNet is particularly resistant to the counterfactual bollocks on sex.
I think some of the confusion in younger generations may be because in the last 50 or 60 years we have to a large extent decoupled the act of sex from its primary evolved reproductive purpose. And that's obviously great - the positives in terms of gay rights and women's liberation is enormous! But evidently it's left some people weirdly liable to missing the obvious.