What is a good argument against "sex is a natural contract" for?
Smoking is a natural contract for lung cancer. Therefore nobody who gets lung cancer from smoking (or liver failure from alcoholism or a broken leg from skiing or or or) should be able to access treatment. Right? They just have to suffer the consequences of their actions. In other words, translate the principle into a context that has nothing to do with sex or with women, and see how valid it is. (Spoiler: Just about all anti-abortion arguments fail this test.)