I’ve been discussing the moral argument for the existence of God lately which goes simply:
If God does not exist, objective morals do not exist.
Objective morals do exist.
Therefore, God exists.
A quick and standard rejoinder has been, “So you’re saying atheists can’t be moral?” Now on its face, the question is a straw man, and a poorly phrased one at that. What the question should be is, “Does the moral argument imply that atheists cannot behave in socially well-adapted way?” Or in other words, “Can’t atheists be nice folks?” And of course the answer to that (irrelevant) question is “no.”
But it raises another question that is not addressed by the moral argument. That question is, “Can atheists rationally commit to binding behavioral obligations that they are not free to violate without hypocrisy or deceit?” In other words, is there anything that rationally makes atheists be nice folks. And the answer to that is a solid “no.”
Without God, the universe is a mysterious accident. Life is an accident. The fact that we can contemplate our existence and wonder about our purpose is a horrible disfigurement of human nature brought on by runaway genetic mutation. Thinking about purpose in a world that has none can only lead to despair. As a result, our deaths are meaningless conclusions to the senseless banging together of the particles that comprised our bodies. If we die young, it is neither right nor wrong. If our lives accomplish nothing, it is neither right nor wrong. If we hurt others or are hurt ourselves, there is nothing fundamentally right or wrong about the hurting. Wanting to improve humanity is a silly misfiring of genetic inclinations to preserve ourselves, all of which will be rendered utterly stupid when the universe eventually expands to the point of its inevitable heat death.
So must the atheist be nice? By no means! And it is not wrong for him to be mean, because in the atheist conception, there is no real right or wrong. There is only impulse, social contract, and group think.
These questions would come a lot more clear if we would start defining morality as a logically obligatory set of behavior-governing principles, at which point we could say definitively that atheists cannot be moral. They can only be nice. And their reasons for doing so may as well likewise die an early heat death.
Can atheists be moral? Not by this definition. They can go along with the group will of the day, constantly open to the option of abandoning public consensus for the sake of personal gain or pleasure. And the most casual study of human behavior will show how likely that possibility is.