“Why be moral?” was basically the question Thrasymachus put to Socrates. According to Thrasymachus, the ideal life would be to have a reputation for perfect justice while being completely unjust. That way you could enjoy all the advantages of injustice while basking in the glow of a good reputation. Socrates had to show that it would be better to be perfectly just even at the price of being thought unjust. Of course, the Christian could say that the unjust man will face judgment in the hereafter, and that this is a reason to be just. However, this misses the point. The question “Why be moral?” is not asking for a prudential consideration. It poses the metaethical question “What is the source or ground of moral obligation?” In other words, why ought we to do anything?
There are two ways a Thrasymachus could defy us to show him that there are genuine moral obligations. One would be to defend moral skepticism, i.e., to argue that there may be truths about right and wrong, but that these cannot be known. The second would be to assert moral nihilism, the claim that there are no true ethical principles. I shall focus on this second option here.
Moral nihilism holds that ethical judgments do assert cognitive claims, so that emotivists and other noncognitivsts are wrong to think that ethical utterances merely express feelings or commitments. Yet, nihilism holds that all such claims are in fact false. One prominent nontheist, J.L. Mackie, did adopt a form of moral nihilism. According to Mackie’s “error theory,” we all tend to think that there are true ethical principles, but we are wrong. Therefore, no answer can be given to Thrasymachus. Now from a “public relations” standpoint, it might be bad for nontheists to adopt such nihilism. But so what? Nontheism will never be as popular as theism. Besides, in the true spirit of Socrates, we should value truth rather than popularity.
Still, many nontheists would repudiate moral nihilism and defend some form of ethical objectivism, i.e., the view that some things just are–universally–right or wrong. Here it is important to distinguish ethical objectivism from moral realism. Moral realism holds that ethical principles are universally valid independently of human choices. One can be an ethical objectivist and still hold that ethical principles are in some sense constructed by human choices, or at least hypothetical choices. John Rawls is a case in point. He famously asks what sorts of moral rules we would have chosen if, prior to being born, we had been placed behind a “veil of ignorance” where we would have no knowledge of our future status. That is, we would not know whether we were destined to become a prince or a pauper, attractive or ugly, strong or weak, brilliant or slow, educated or illiterate, or anything else that would give us advantages or disadvantages vis-a-vis others. In such a situation, Rawls argues, we would all opt for justice and fair play, with certain inalienable rights and equal chances for all to compete for life’s goodies. Why be just? Because that is what each of us would have chosen had we decided from behind the veil of ignorance.
But can moral realism be defended from a nontheist position? Clearly it can. One could be an intuitionist and hold that rightness or wrongness are objective, non-natural properties that supervene upon certain acts, policies, etc. Such intuitionism has been regarded as metaphysically extravagant by its critics, but it certainly seems no more extravagant than to invoke the God of the “omni” predicates as a basis for moral realism. For the intuitionist, a Thrasymachus suffers from a failure of his intuitive faculties; he is like a person born blind. Anyone with normally functioning intuitive abilities will just see, e.g., that the gratuitous infliction of harm is intrinsically wrong and therefore ought not to be done.
Of course, intuitionism is only one of many options. One could also take the Kantian line that the fundamental rule of morality, the categorical imperative, is simply a deliverance of reason. In this case, a Thrasymachus who demands to know why he should act only on that maxim that can consistently be willed to apply universally, would just be missing the point.
Now it is well known that none of the standard ethical theories is without problems. Still, it is hard to see that the nontheist, qua nontheist, is at any special disadvantage here. No ethical system has won anything like universal agreement, not even (perhaps one should say especially not) ones that invoke theism. For instance, natural law theories have few advocates outside the Catholic Church. The moral nihilist has the job of showing that all these theories are false or at least implausible. That is a heavy enough burden, but even that is not enough to support nihilism. The nihilist has the task of showing that judgments like “it is wrong to inflict gratuitous harm” are reasonably thought not true, not merely that no ethical theory has yet shown why they are true. With all due respect to the late, great J.L. Mackie, I do not think this has been done.
Now I may have gotten Thrasymachus wrong so far. It could be that he is not doing anything as profound as asking the metaethical question about the grounds of moral obligation. The answer to that question would be to give an acceptable metaethical theory, the sort of answer I outline above. It could be that Thrasymachus is just a dull immoralist who is saying “Even if x is the right thing to do, I don’t care. Nyah Nyah!” There just is nothing philosophical to say to such immoralism because it is beyond reason. We might invoke prudential considerations as a motivation. Here theists definitely have an advantage since they can threaten hell (though people seldom think that hell is for them). All nontheists can do is point out, correctly I think, that bad people usually have rotten lives. Even if they die rich, they usually die unloved. They can buy sex from prostitutes or trophy wives, but not affection. They may be surrounded with sycophants, but will have no real friends. Their lives are filled with suspicion, anxiety, cynicism, disappointment, and loneliness. Thrasymachus’s tricks may work for a while, but, as Lincoln sagely observed, you cannot fool all the people all the time.
In summary, the question “Why be moral?” strikes me as a nonproblem, or at least no more of a problem for the nontheist than for the theist. Each can address the problem only by developing an acceptable metaethical theory, and it is not clear that this has yet been accomplished by anyone. It is even less clear that the theist will have an easier time developing one than the nontheist.