Basically, every person has ethical intuition that certain acts and behaviors are wrong because they are unnatural. For example, we perceive by intuition that the normal and natural sex partner of a human is another human, not an animal. The same reasoning applies to the case of homosexual behavior. The natural sex partner for a man is a woman, and the natural sex partner for a woman is a man. That is why people have the corresponding intuition concerning homosexuality as they do about bestiality- that it is wrong because it is unnatural.
Do we now see the reasoning in natural law? This is the basis for almost all standard moral intuitions. For instance, it is not difficult to understand that destruction of human life or infliction of physical and emotional pain is immoral. Who does not understand that? Each human being naturally possesses the dignity and value to preserve life. To destroy life is intuitively immoral. That is why there are specific principles like the unacceptability of murder, kidnapping, mutilation, physical and emotional abuse, and so forth. (To be continued)