Hi David. As I see it, God provides the objectivity even if you only view him as the Logos, or the divine reason implicit in the cosmos. Thus, rape, murder, and genocide are objectively evil. The problem comes when we disagree on what’s the objective truth. Good Catholics, for example, can disagree about the use of the bombs, even though we agree that the Church holds the truth to its fullest. I am persuaded that the arguments against the bombs use on Japan most closely follow the true teachings of the Church. We must, in the end, follow our own informed consciences.