General question about the possibility of objective moral truth

[TheRocketSurgeon]

Thank you for your answer!
About different moral ideas in different cultures: I don't think that we can say that there are such big differences. Your example of the Inuit illustrates that: They kill people who eat human meat. That's really not that far from our thinking. Of course we are not as wild anymore as the Inuit. We don't kill someone who eats human meat. But we send him to prison for sure. Because also in our culture it is seen as a really terrible thing to eat human beings.
And the same you can see in cultures of the past. There have been differences between their moralities, but these have never
amounted to anything like a total difference. If you compare the moral teaching of, say, the ancient Egyptians, Babylonians, Hindus, Chinese, Greeks and Romans, you will see how very like they are to each other and to our own.
Men have differed as regards what people you are supposed to be unselfish to—whether it was only your own family, or your fellow countrymen, or everyone. But they have always agreed that you are supposed 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 have always agreed that you must not simply have any woman you liked.
But the most remarkable thing is this. Whenever you find a man who says he does not believe in a real Right and Wrong, you will find the same man going back on this a moment later. He may break his promise to you, but if you try breaking one to him he will be complaining "It's not fair". A nation may say treaties do not matter, but then, next minute, they spoil their case by saying that the particular treaty they want to break was an unfair one. But if treaties do not matter, and if there is no such thing as Right and Wrong what is the difference between a fair treaty and an unfair one? Have they not let the cat out of the bag and
shown that, whatever they say, they really know about the truth of this rules just like anyone else?

No one says he "does not believe in a real Right and Wrong", but a moral relativist says that different cultures have different ideas about what those rights and wrongs are, making it clear that morality is subjective, rather than objective. You said as much in your reply.

However, because we are a social animal, we have evolved a general sense of empathy for our fellow human beings because this is the only way for social groups to succeed, which manifests itself as a series of "common themes" among the various forms of morality we see in different cultures. Generally, what harms our fellow humans will also harm us if allowed to go on, so we make rules about it.

If you're going to discuss the moral concepts atheists hold with us, we'd ask that you at least try to understand what they are, instead of making up versions that help your argument but which aren't real.