Duh. Thank you for the blinding revelation.
Sex is a situation where the man has the power, which they grant the woman. The power, the physical ability to say no, comes from the man. He grants this power to the woman. While this may not be always literally true, it is psychologically and spiritually true of the sexual relationship between man and woman.
...we will have to agree that rape (as you yourself agreed that it is) is natural. However, this is known to not be the case. Otherwise, instead of the elaborate mating rituals that many different species engage in, the male of the species would simply take the female anytime and any place of his choosing. So, can you explain this disrecepancy?