I would not say that ethical behavior is not possible for the atheist or agnostic. It is. A couple of pretty good examples are Bertrand Russell and Jean-Paul Sartre. However, I will have to say that if we take the human lot as a whole, these two men must be seen as exceptions.
Huston SmithIn the post-individualistic era, science and spirituality will become allies, and human beings will realize a vast potentiality now only dimly felt.
Huston SmithAs the twentieth century began, science equaled a materialistic worldview. As the twenty-first century began, the worldview of science, at least of physics and astronomy, may have traded place with that of religion. Consider Einstein's famous equation E = mc2. Nothing of matter dies but continues on in another form, elsewhere. The church divines and theologians for two thousand years have devised arguments and "proofs" of immortality but nothing equal to this.
Huston Smith