The problem with that, is he is assuming there is a moral law. Morality is no law. Morality is merely a general reflection of societies views at the present time. To say morality is a constant is to deny the fact that moral attitudes DO change. And they do. The Bible, apparently the word of God, condones slavery. Is that to say it is moral to own and work slaves? Certainly not at this time in our existence. While it is an off putting to think that one day, murder might be completely fine, it is not up to us to deny future generations the right to make their own laws. All we are leaving is our structure behind. If they want to modify that model, that is up to them, not us, nor some religious nut jobs and their non-existent sky man.