Conscience....why did ancient pagans sacrifice their children?

Atonement...it is just that some attempts at atonement for rebellion against Natural Law are themselves morally degenerate. The Bible speaks of the Conscience being seared away altogether eventually, but it is like a process. At the end of Conscience you have what one philosopher called a "flat souled" type of person, insensitive, dead in the head. This is the end of civilization too, when there are enough who are dead in the head.

The Conscience, the Word on the individual level,
"...there was the woman of chapter two, who had her first abortion out of anger because her husband had been unfaithful to her, and her second because “I wanted to be able to hate myself more for what I did to the first baby.” In much the same waythat some people use one credit card to pay off another, she was trying to abate her present remorse by increasing her burden of future remorse.

We may be sure that spoiled remorse is just as great a motive for killing the sick and the old. For years, perhaps, I have neglected my aging father. Now, when he is weak and dependent, the burden of my conscience has become intolerable. I cannot bear the reproach of his watery eyes; I would rather endure the blows of his fists than the sight of his withered, lumpy hands. To avoid him I visit him less and less. One day he requires hospitalization and cannot feed himself. He is not dying, he is not unconscious, he is not even in great discomfort; nevertheless I tell his caretakers to withdraw his food and water. It is easier to face them than to face him, for he is the sole surviving witness to the slights of his ungrateful son. Besides, I tell myself, I no longer deserve a father. When his body is buried, perhaps my guilt will be buried as well."
(The Revenge of Conscience: Politics
and the Fall of Man
By J. Budziszewski)

People are still thinking in terms of justice, Good and Evil, all the time. They just convince their Selves that what they are doing is Good. I have done so too. Yet everyone has different limits and we are not all equals in the extent and ways we do so.