It's a common criticism of atheists that they are somehow lacking in the area of morality and ethics, that because they don't have some central religious principles guiding their lives, that their ethics and morality is therefore lacking something important.
The question concerns where we get our morals and our ethical principles from. Of course, the simple direct answer is that we get a lot of it from our parents and immediate family, our peer group, the institutions that educated us, and so on.
Religious people often argue that we have an innate sense of right and wrong, given to us by some deity as a birthright. According to this view, we all have to struggle to live up to some absolute judgement of right and wrong. For them, sin is the expression of this difficulty but people in themselves, already know what is right, wrong, true, false, evil, etc.
Against this view is the atheist position that ethical values and morality are social in origin. Because we grow up in a society that already has a history, the institutions already promote certain values that we grow up with. There are laws, customs, social conventions, which are based on certain shared values, and as a result, we can generally see the point of social judgements of right and wrong. The familiarity makes things seem ethically obvious.
But when we take those values and look at another society, or our own in the past, those values don't seem to fit.
Take the example of slavery. Right until the nineteenth century, western countries considered slavery to be the natural order of the world, something not just unobjectionable but quite reasonable. Many prejudiced social theories were promoted as obvious justification for using slaves. There was nothing in the Bible or the Qur'an arguing against slavery and as these books were regarded as moral authorities by the religious, there was no religious teaching opposing it.
We could argue that slavery is wrong - absolutely and unconditionally. Most of us, hopefully, would agree with that statement as an expression of what we think. And yet with equal certainty, the clerics of the early nineteenth century would have argued that it is not. From our position, we declare them to be wrong. Every age believes its values to be objective, absolute, immutable, true.
Given the certainty with which each age declares its ethical values, how can we explain how they all seem to think they are right? The answer is that there are no absolute ethical values - slavery was right to their eyes, wrong to ours.
We can argue that as we better understand our natures, as we improve our mastery of science and technology, as we become more sophisticated in analysing our motives and interests, we reduce the irrationality of some of our moral and ethical judgements. We expose the prejudices and false assumptions.
So moral relativism, far from being immoral or unethical, roots both in social reality. For a moral relativist, moral and ethical judgements have to be justified in social and political terms and cannot rely on words from an old book, or statements from a cleric such as a pope. They have to have a rational ethical basis, they cannot be arbitrary.
Every age confronts its ethical questions with a mixture of the values it has inherited combined with the critical thinking of those looking for better reasons. By challenging the values of the past, we not only ensure that ethics are relative and relevant but we also put ethics in its political context.
Religion doesn't contribute anything to this process - it acts as a brake on ethical thinking because it has to relate ethics to a dogma and always pulls backwards. So far from the religious having a superior ethics and morality, they are far less able to adapt and be critical. Moral relativism is actually a realist, materialist, philosophy which insists on higher standards of ethical reasoning, rejecting the arbitrary statements of religious books, and insists on a critical attitude to received values and our historical legacy.
