So, I'm going to argue that this is an illusion -- that the separation between science and human values is an illusion -- and actually quite a dangerous one at this point in human history. Now, it's often said that science cannot give us a foundation for morality and human values, because science deals with facts, and facts and values seem to belong to different spheres. It's often thought that there's no description of the way the world is that can tell us how the world ought to be. But I think this is quite clearly untrue. Values are a certain kind of fact. They are facts about the well-being of conscious creatures.In other words, Harris claims that right and wrong are about what promotes the flourishing of human beings and that science can speak to this question. There are, however, at least three things wrong with using human flourishing as a criterion for ethics:
1. On what grounds do we privilege human beings over other animals? What works against human flourishing (e.g. mass slaughters) might be a boon to the flourishing of animals, particularly carrion-eaters. On atheism, then, what grounds are there for the specieist promotion of human flourishing over that of the flourishing of other animals in general and other mammals in particular?
2. Whose idea of flourishing do we promote? What promotes human flourishing in the mind of a member of ISIS who thinks the human race would be better off if everyone were forcibly converted to Islam or killed might be distinctly immoral to say, Sam Harris. Whose conception of human flourishing should we privilege and how do we decide that?
3. On what grounds does an atheist conclude that I should be concerned with the flourishing of others as opposed to simply my own flourishing? If I can flourish at the expense of others why would that be wrong? Why is it wrong for me to flourish by exploiting the earth's resources and letting future generations yet unborn to fend for themselves?
Perhaps Harris can answer these questions, but I have serious doubts. Atheism simply does not supply the philosophical resources necessary to support a belief in objective moral obligation. If atheism is true morality devolves to subjectivism, i.e. the view that what's right is whatever I feel is right or whatever I feel I should do, and subjectivism offers no rational justification for stopping short of a "might-makes-right" view of ethics.
On atheism, whoever has the power to make the rules gets to make them, whatever they are, and there's nothing wrong with that.