How can there ever be evidence for physical (psychophysical) harm to children who watch adults have sex? We 're like the only species who copulate in private, s

How can there ever be evidence for physical (psychophysical) harm to children who watch adults have sex? We 're like the only species who copulate in private, so it seems hugely presumptuous to argue that it is harmful. I think the greater harm is done by the continuous brainwashing with messaging that suggests that sex is the ultimate reward and is somehow connected to your value as a person, and is a thing you can trade.