Just maybe his lack of understanding on this and moral relativism comes from his theory that there is no God and therefor no moral absolutes.
Let's see . . . I don't want to start a debate so I'm going for focus on sharing my feelings . . . I'm an atheist. I have friends who are atheists. None of us are amoral. There are other foundations for morality besides divine command (I'll expound further on this if you are interested, but not here). My point here is that the implication that a lack of belief in a god leads to inferior morality is unfair and offensive.
"As long as the child within is not allowed to become aware of what happened to him or her, a part of his or her emotional life will remain frozen . . . all appeals to love, solidarity, and compassion will be useless."
-- Alice Miller