You’re asserting your point from a (rightful) assumption of moral absolutes, that moral right and wrong exist beyond human creation and definition.
If you want to understand his point, (temporarily) suspend that assumption of objective (God defined) morality.
But to do that you must suspend all reason and attempt to argue from a position of absurdity. Once you eliminate God the concept of "morality" is meaningless and consists of nothing more than personal preference or social convenience - neither of which has any necessary claim to my allegience.