That's why I like her work, she starts from fundamentals. Christians say everyone is a sinner and needs Christ. Ayn Rand agreed - and then observed that most people do NOT receive Christ in their hearts. So she simply asked, okay, how would such people, who refuse Christ, act? What WOULD govern their behavior? How would they justify it? What would they actually do?
Simple, but brilliant.
I wished Ayn Rand had even been mentioned in high school. I would have read Atlas then which was the 80s.