“When gentiles (non-believers) who have not the law do by nature what the law requires…they show that what the law requires is written on their hearts while their consciences also bears witness ….” (Romans 2 :14-15)
All of mankind is made in the image and likeness of God. It is part of that likeness to naturally have a sense of right and wrong, justice, mercy, etc. Whether someone believes in God or not, we all have a conscience that speaks when doing right or wrong. This is not a social construct. We can feel shame for doing wrong even though society may praise us for it. And we can feel satisfaction for doing right even though society may accuse us of wrongdoing.
Many times we have conflicting feelings about something. Our conscience is telling us one thing, and society or our own desires want the opposite. It is for this reason that God gives revelation and especially the commandments, so that we can KNOW what is right and wrong. The better informed our conscience is, the better it can be formed. The better formed the conscience is, the better it can know what is good, and not just what is perceived to be good.
An unformed conscience will tend to stick with the basics like the Golden Rule. This can provide an acceptable basis for man and society, but it is kind of the “live and let live” or “I won’t bother you if you don’t bother me” attitude. It also has a common selfish aspect which is “if you can’t help me, I won’t help you”. However a formed conscience with God as the “moral compass” will go beyond the Golden Rule because God commands us to actually love one another with specifications of HOW to love one another, which always involves actually doing what is good for the other person, regardless of what we may perceive (correct or incorrect) to be good. Easier said than done.
I believe it was St. Thomas Aquinas who said “when given a choice, man will always choose the good, even if it is only a perceived good”. In order to choose “evil”, we have to justify it by saying there is some sort of “good” in doing that. Having God as the moral compass can tell us regardless of the perceived good or how we can justify something as good, it is still evil so don’t do it. Hitler had to justify doing evil by promoting the perceived good of the human race, but it was still evil.
Another thought: All of creation has laws. Planets and material things are subject to laws of gravity, motion, etc. Animals have specific laws of instincts that they live by. Humans are the only creatures that can actually disobey or go against the laws written in their hearts. All of nature works very well together according to the laws that apply to them. The moral laws are written into our hearts so that we can be the best human person that we can be. The moral laws are for our own wellbeing. When we break them (even if it is unknowingly), we harm ourselves and others (also possibly unknowingly). That is why it is essential to have the Law Giver as our moral compass; so that we can know and do what is good for ourselves and others as well as society as a whole and nature. This leads to a life of joy, harmony, and fulfillment. The less we have the Law Giver of all things as the moral compass, the more likely we are to hurt ourselves and others by going against those moral laws.
More than my allotted 2 cents worth.