Having discussions with Atheists and Humanists about morality can prove to be frustrating, for everyone involved. On the one hand you have Theists who argue that the skeptics cannot properly ground morality given Naturalism. Skeptics often understand this to mean ‘Atheists cannot behave morally unless they believe in God’. But no one here is making that argument. We all know there are Skeptics who are kind and charitable. On the other there is the skeptic, who attempts to show how no transcendent standard is necessary i.e., altruism and nurturing helped groups and individuals survive. Thus behaving ‘morally’ is adequately explained on a naturalistic worldview. The problem seems to be the words good and bad, and how the skeptic employs them.
The way many — if not most — skeptics use the words good and bad is not the same way a Theist is using those words. The Theist uses these terms with an understanding of ontological rightness and wrongness. The skeptic seems to be using these words in a functional or utilitarian sense. The goodness or badness of something is dependent on the beneficial or disastrous result. If the act is helpful to someone, or makes them generally feel good or happy is good. If the act hurts or harms, it is bad.
What makes this confusing is the skeptic will most often have in mind the Theist’s understanding, but ground it and describe it with an evolutionary foundation. This doesn’t work because of the logical exclusion of morality on the Naturalistic worldview (see: Who Needs Morality?).
The terms good and bad are used equivocally. In one sense, they are intended to be understood ontologically. However, they are defended and used functionally. Like moves in a game in chess, there are good moves and bad moves. The good moves (moral behavior) achieve the goal, capturing the opponent’s king (flourishment of the human species). But this isn’t morality. It’s utility couched in moral language.
This is made clear by asking the question: Why should someone do the morally good thing? If the answer employs culture or society, that is relativism, which isn’t morality, it’s preference. If the answer appeals to flourishment, that is a form of utilitarianism, not morality.
Without an unchanging standard that is outside the person — culture and society is nothing more than many individuals — only to preference and functionality can an appeal be made. Preference holds no real authority. It describes what most people want. But what is morally good is not determined by a vote. Sometimes what the majority of the people want is morally evil i.e., the enslavement of Africans in early America, or the Roman Gladiators fighting to the death for entertainment. Functionality only tells us what works, like driving directions. Directions are not morally good or bad, they are useful or unuseful.
Of course, not being able to explain moral goodness and badness doesn’t mean atheism is false. It merely exposes its inadequacy to account for the way the world is.