Honestly, this conversation shouldn’t take that long. But it rages on and on, because theists who try to convince non-theists that a god must exist always seem to come around to the tired argument, “What about your moral compass? Where do you think that comes from?” The assumption being made is that since we know right from wrong, there must be a god who instilled those values in us.
The short answer to this argument is simply, Ethic of Reciprocity. Christians know it as The Golden Rule, and they’re often surprised to learn that the concept long predates Jesus. It appears in philosophic models and religions like Buddhism, Confucianism (both ~5th-century BCE), and Hinduism (which evidence dates as early as 1700 BCE). It is really a very simple idea: do things to others such that, if they reciprocate, you won’t be hurt. It’s a survival thing. I wasn’t there, but I’d be willing to bet early humans had to learn the lesson the hard way. But then they taught their offspring, who taught their offspring, who eventually went off and formed societies (and religions) with the wisdom of the ages to date. This is where right and wrong come from – our ancestors who had to learn the hard way. I mean really, have right and wrong changed much since the dawn of man? Or at least since man started recording his ideas?
Morality does not have to be a religious principle. It is easy to assign this to God, especially if you are raised to believe that the ten commandments are a moral code issued by God Himself. If that’s the case, consider opening your mind to a different source of societal ideals.