Atheism and Ethics

If I had taken a college course on ethics, I might know whether R. Avi Shafran's statement that Atheists have no compulsion to be ethical ("If our perception that some deeds are good and others are not is but a quirk of natural selection, none of us need feel any commitment to morality or ethics" - link) is contradicted by the writings of Immanuel Kant, John Stuart Mill, Jean-Paul Sartre and others. Maybe someone who is educated in these matters can explain this to me.