The idea in the biblical tradition of the Fall is that nature as we know it is corrupt, sex in itself is corrupt, and the female as the epitome of sex is a corrupter.
This is the Manichaeism heresy - material world = evil; spiritual world = good. The actual Biblical view is that everything God creates is good, but as moral agents we can use things against their nature like premarital sex. In this example sex is not corrupt, but us the moral agent is corrupted by orginal sin.
