"...If anyone will take the trouble to compare the moral teaching of, say, the ancient Egyptians, Babylonians, Hindus, Greeks, and Romans, what will really him will be how very like they are to each other and to our own." (C.S. Lewis, Mere Christianity, p. 6)
This factor certainly is a powerful support of the moral argument for the existence of God. It shows that He has inscribed His moral laws into our hearts. If moral relativism is true, then it would be difficult to imagine how something like the golden rule (i.e. love your neighbor as yourself) can be found in ancient human civilizations outside the Judeo-Christian framework.
"...Men have differed as regards what people you ought to be unselfish to-whether it was only your own family, or your fellow country men, or everyone. But they have always agreed that you ought not to put yourself first. Selfishness has never been admired. Men have differed as to whether you should have one wife or four. But they always have agreed that you must not simply have any woman you liked." (ibid. p. 6)
This seems to point to a moral Law Giver, with the problem being our sin nature that we inherited due to the fall of Adam and Eve. Lewis provides examples such as the condemnation of selfishness and the regulation of sexual behavior. These examples further support the idea that certain moral principles are universally recognized.
"...surely the reason we do not execute witches is that we do not believe there are such things. If we did-if we really thought that there were people going about who had sold themselves to the devil and received supernatural powers from him in return and were using these powers to kill their neighbors or drive them mad or bring bad weather-surely we would all agree that if anyone deserved the death penalty, then these filthy quislings did? There is a difference of moral principle here: the difference is simply about a matter of fact. It may be a great advance in knowledge not to believe in witches: there is no moral advance in not executing them when you do not think they are there. You would not call a man humane for ceasing to set mousetraps if he did so because he believed there were no mice in the house" (ibid. p. 14-15)
The discussion about executing witches illustrates how changes in belief about facts (e.g. the existence of witches) do not change moral principles. This suggests that our moral expectations and actions are grounded in objective truths.