But if a 26-year-old man had sex with a 17-year-old girl in your extended family, you'd want to string him up because she might be attached to him.
By George, I think you’ve got it!
Reality is, I think, encoded in traditional social systems and attitudes. Girls/women require extra protection in these matters, because they are much more vulnerable in many ways.
Tradition is a true guide, liberal idealism isn’t. Again, see Edmund Burke.