Some people believe that there cannot be progress in Ethics, since everything has been already said. Like Rawls and Nagel, I believe the opposite. How many people have made Non-Religious Ethics their life's work? Before the recent past, very few... Buddha may be among this few, as may Confucius, and a few Ancient Greeks and Romans. After more than a thousand years, there were a few more between the Sixteenth and Twentieth centuries. Hume was an atheist who made Ethics part of his life's work. Sidgwick was another. After Sidgwick, there were several atheists who were professional moral philosophers. But most of these did not do Ethics. They did Meta-Ethics. They did not ask which outcomes would be good or bad, or which acts would be right or wrong. They asked, and wrote about, only the meaning of moral language, and the question of objectivity. Non-Religious Ethics has been systematically studied, by many people, only since the 1960s. Compared with the other sciences, Non-Religious Ethics is the youngest and the least advanced...
[In the long-term future,] there could be higher achievements in all of the Arts and Sciences. But the progress could be greatest in what is now the least advanced of these Arts or Sciences. This, I have claimed, is Non-Religious Ethics. Belief in God, or in many gods, prevented the free development of moral reasoning. Disbelief in God, openly admitted by a majority, is a recent event, not yet completed. Because this event is so recent, Non-Religious Ethics is at a very early stage. We cannot yet predict whether, as in Mathematics, we will all reach agreement. Since we cannot know how Ethics will develop, it is not irrational to have high hopes.
-- Derek Parfit, Reasons and Persons, pp.453-454.
See also my post: Moral Diversity and Skepticism.