What Atheism, by design, lacks is a counter to the ring of Gyges. The secular reason I have for resisting a turn away from religious to secular morality is exactly that. I can never have a ring of Gyges; God is always watching. Indubitably many people won't become heinous when given total anonymity in real life, but a religious motivation is stronger than a secular motivation when it comes to the ability to do evil and no one would know.