@AtheistAdvocate Thanks for your thoughtful comments.
I believe I understand what you're saying with the humor analogy, and the point I take it to make is that we have to have an understanding of a term before we can reason about it, discuss it, etc. If we had no concept of humor, it wouldn't make any sense for someone to tell us that God has a maximally great sense of humor (and I think he probably does).
But to see the difference between this and the point I want to make, we have to distinguish between moral epistemology and moral ontology. Your analogy relates to moral epistemology--how we come to understand the ideas/concepts of good and evil. On that question, I think there are several sources--our families, society, ideas from scholars and thinkers, and especially, in my view, that we are made in God's image and thus have an innate moral orientation.
But the question of moral ontology is what constitutes the ontological basis for right and wrong--what grounds it, what makes it the case that something is objectively good or evil. By objective, I mean mind-independent. For example, if everyone in my country believed it was right to discriminate against a minority race, that would still be wrong, even though everyone believed it was right.
In your example about honesty, it's true that people generally prefer a society where honesty is the rule rather than the exception. But because this judgment depends solely on a generally held opinion or a widespread belief among human beings, it's ultimately subjective. If there's no objective standard "out there" to appeal to, we're just left with relativism (my opinion against yours).
Let's say I'm a criminal and want to survive by stealing from others. I too will prefer an overall condition of honesty, because it makes me safer, but I know I can benefit from dishonesty as long as I'm not caught. What can be said to persuade the criminal not to steal?
Without objective morality, you can tell him that most people don't like it, that it goes against the grain, that it gives other people a bad feeling---but you can't tell him that he's objectively *wrong.* It would be like trying to tell someone their preference for chocolate is wrong and the preference for vanilla is right. We have no higher standard to appeal to in this case---nor in the case of moral questions where there's no mind-independent norm.
If we all we have is naturalism, the situation is even worse, because in this case we're trying to come up with values when all we have is matter, energy, and laws of nature. You won't find a single physics textbook that describes an entity called a "moral value," because morality can't be reduced to elementary particles--but that's all you've got on naturalism to work with.
I mentioned earlier that a number of atheists concede this point, and I'll give a few examples:
"In a universe of blind physical forces and genetic replication, some people are going to get hurt, and other people are going to get lucky; and you won't find any rhyme or reason to it, nor any justice. The universe we observe has precisely the properties we should expect if there is at the bottom, no design, no purpose, NO EVIL and NO GOOD; nothing but blind pitiless indifference."
- Richard Dawkins, "River Out of Eden: A Darwinian View of Life”
“We have not been able to show that reason requires the moral point of view, or that all really rational persons should not be individual egoists or classical amoralists. Reason doesn't decide here. The picture I have painted for you is not a pleasant one. Reflection on it depresses me . . . Pure practical reason, even with a good knowledge of the facts, will not take you to morality.”
- Kai Nielsen (atheist philosopher), "Why Should I Be Moral?" American Philosophical Quarterly 21
“Let me summarize my views on what modern evolutionary biology tells us loud and clear — and these are basically Darwin’s views. There are no gods, no purposes, and no goal-directed forces of any kind. There is no life after death. When I die, I am absolutely certain that I am going to be dead. That’s the end of me. There is no ultimate foundation for ethics, no ultimate meaning in life, and no free will for humans, either.”
- William Provine, Professor of Biology, Cornell University
"The central question about moral and ethical principles concerns their ontological foundation. If they are neither derived from God nor anchored in some transcendent ground, they are purely ephemeral."
- Paul Kurtz, founder of the Council for Secular Humanism, "Forbidden Fruit," p. 65.
"If there is no single moral authority [i.e. no God] we have to in some sense 'create' values for ourselves ... [and] that means that moral claims are not true or false… you may disagree with me but you cannot say I have made a factual error."
- Julian Baggini (atheist philosopher), "Atheism: A Very Short Introduction" pp.41-51.
"The existentialist, on the contrary, finds it extremely embarrassing that God does not exist, for there disappears with Him all possibility of finding values in an intelligible heaven. There can no longer be any good a priori, since there is no infinite and perfect consciousness to think it. It is nowhere written that 'the good' exists, that one must be honest or must not lie, since we are now upon the plane where there are only men. Dostoevsky once wrote: 'If God did not exist, everything would be permitted'; and that, for existentialism, is the starting point. Everything is indeed permitted if God does not exist, and man is in consequence forlorn, for he cannot find anything to depend upon either within or outside himself."
- Jean-Paul Sartre, "Existentialism Is a Humanism," p.28
On theism, however, morality is grounded in God's nature, and His commands constitute our moral duties. If you agree with me that morality isn't just an illusion, that's a good reason in my view to believe that God exists.
Look forward to hearing your thoughts.