From a purely rational perspective, why can't children have sex (in particular, with adults)?
It seems the number one response is always 'they can't consent'. But what does that mean and what does it entail?
When people say 'they can't consent', how is that true? It can't mean that they can't voluntarily participate as an act of will, because they can. Even if the vast majority wouldn't (for natural lack of sex drive for instance), why couldn't some of them? Usually the 'they don't understand it' argument follows this but why not? Is sex astrophysics? Why can't you explain how it works then tell them it can be dangerous if you don't take a few basic precautions like condoms and generally not pushing your limits? I mean, swimming in a lake could be dangerous too, you could drown for instance, but no one says 'children can't go swimming because they can't consent to it because they don't understand it and it's dangerous!'
I suppose the last resort would be ' it will mentally scar them for life!', but how do we know this isn't due to the social variables and taboo nature of it? Maybe they become 'scared' because they are told after the fact how traumatized they ought to be. Maybe it's all police and courts and therapists that get thrown at them that causes them mental anguish.