Can an atheist be moral? Yes, of course, in one sense, and indeed more moral than some theists. But the more interesting question would be whether an atheist would have an objective basis for an objective morality. In other words, even if it is true that many atheists are morally superior to many theists relative to some agreed-upon standard of behavior, would these atheists be justified in making the moral judgments they do if there is no God? Perhaps, but the answer to this is not obvious, whereas the answer to the first question is obvious.
While there are those who have tried to devise such a scheme, I think their efforts are misplaced; I will not try to establish an “objective morality” here, because I see no need for one.
First, we should note that to the atheist the supposed bedrock upon which theists base their moral framework — the word of God — is an illusion anyway, so there is no compelling evidence for their claim to a truly objective morality. To the nonbeliever, one of two things must be happening: either the theist is simply following orders from a set of texts and teachings that are quite contingent and arbitrary as regards their content, or those texts and teachings actually codify a moral sense that generally exists in us anyway, and the veneer of Divine origin that is applied to these moral precepts is simply a social mechanism that intensifies the pressure to conform, and provides a mechanism to resist change over time, an anchor against drift.
My feeling is that the second description is essentially the case, and I think that this is indicated by the fact that even those who argue most vociferously that an objective moral code is necessary, and that this code can be found in Scripture, seem nevertheless to pick and choose according to their own innate moral compass. For example, Exodus suggests that a child who smites his parent must be put to death, and that we must not suffer witches to live. The Old Testament is liberally peppered with harsh injunctions of this sort, but you would be hard put to find a theologian these days who argues that such premises should be part of our moral repertoire, even though they are allegedly clear instructions from God. Stoned an adulteress lately?
The fact is that the everyday moral decisions we make are not weighed against a set of absolute rules, but rely upon, as Patricia Churchland has put it, a set of social “skills” that we are predisposed to as part of our genetic legacy, and which are further refined and personalized by our social context and individual history. There are indeed moral precepts that appear to be human universals, and which are likely part of our evolutionary heritage: proscriptions against murder and incest, for example, are found in all cultures. Other layers of morality vary from culture to culture, or, within cultures, from era to era — some quite strikingly so, as in the changing attitudes here in America having to do with slavery, for example. (The God of the Old Testament, by the way, seems quite untroubled by slavery; see, for instance, Leviticus 25:44.)
But if we have no objective basis for morality, must we then slip into a grey and relativistic worldview in which we have no justification for condemning what we see as the immoral acts of other groups? Absolutely not. If we view, say, female genital mutilation as morally wrong because of the suffering it inflicts on subjugated and helpless girls, then there is no reason why we should not work for its eradication. The fact that no moral system may ultimately rest on objective bedrock does not mean that we must abandon our particular moral intuitions. If we prefer to live in a society where such cruelty is not practiced, why would we not act accordingly? Should we freeze in our tracks because we consider ourselves incapable of making moral decisions on our own, in the absence of a supernatural authority figure, a Heavenly Father, to sign the orders? It’s time we grew up, and began to take some responsibility for ourselves.
Finally, the absence of an objective basis for morality in the absence of God is sometimes trotted out in defense of theism itself; a notion that clearly has things backward. Even if it were impossible to live morally guided lives in God’s absence — and I am quite certain that it is not — the fact would not in itself constitute evidence for God’s existence. Arguments based on such preferences — on how we would rather that things be, or that they must be a certain way because it would be awful if they were otherwise — are worthless. What we want, of course, is the truth.