Except for the brief period of time I tried to convince myself atheism made sense, I have always thought there is more to this universe than just matter and energy.
If our bodies and brains are nothing but the deterministic motions and chemical reactions of electrons, then we might as stop talking about morality. Morality is just an illusion, and we're kidding ourselves by saying there is any such thing as morality.
It's just preferences and opinions.
History is pregnant with examples of people who got ahead by lying and cheating.
Plenty of societies thought it was absolutely necessary to sacrifice children, have slaves, abandon babies, practice female infanticide.
It's only our opinions that those things are absolutely wrong in a materialistic worldview.
Oskar Schindler did not risk his life to save the lives of thousands of strangers because he was thinking about how to make society stable. He did it because his conscience apprehended absolute good from evil.
It is absolutely false that what we consider conventional morality just comes to us naturally. Trying to live a life completely free of lying, cheating, greed, selfishness, sexual immorality, self-centered vanity, resentment, hate, etc. is virtually impossible, even though our conscience tells us what we ought to be doing.