a) homosexuality is not unnatural and there is not necessarily observable behavior indicating if a person is gay. if you have a son, there is a chance he might be homosexual, that is just how nature works.Homosexuality is unnatural so no father is gonna assume their kids will be involved that sort of fukkery unless they see questionable behavior. While heterosexual sex is natural and every father knows that around those teenage years is when kids start wanting to have sex so its normal to wanna start safeguarding your daughters around that age.
b) if wanting sex is natural, why do you need to traumatize your daughter to stop her from having it?