One of the most controversial parts of the movie Expelled: No Intelligence Allowed was the segment where Ben Stein interviewed the history professor Richard Weikart about his book, From Darwin to Hitler: Evolutionary Ethics, Eugenics, and Racism in Germany.It's a tragic historical fact, demonstrated repeatedly throughout the last two centuries, that once people reject the idea that morality is rooted in an omnipotent, omniscient, omnibenevolent and transcendent personal being the next logical step is to abandon the idea that there's any objective moral right and wrong at all.
Darwinists were apoplectic, deriding Stein and Weikart for daring to sully the good name of Charles Darwin by showing how Hitler, and German scientists and physicians, used Darwin's evolutionary theory to justify some of their atrocities, such as their campaign to kill the disabled.
Some critics even denied that the Nazis believed in Darwinism at all. Weikart challenges his critics to examine the evidence in his fascinating sequel, Hitler's Ethic: The Nazi Pursuit of Evolutionary Progress, which examines the role of Darwinism and evolutionary ethics in Hitler's worldview.
In this work Weikart helps unlock the mystery of Hitler's evil by vividly demonstrating the surprising conclusion that Hitler's immorality actually flowed from a coherent ethic. Hitler was inspired by an ethic based on the evolutionary history of man to pursue the utopian project of biologically improving the human race. Hitler's evolutionary ethic underlay, or influenced, almost every major feature of Nazi policy: eugenics (i.e., measures to improve human heredity, including compulsory sterilization), euthanasia, racism, population expansion, offensive warfare, and racial extermination.
This step is inevitable since nothing else but such a being as described in the previous sentence could possibly provide a basis for objective morality, and once this step is taken it leads inevitably to moral arbitrariness and subjectivity. In other words, what's right is whatever feels right to me. Moral subjectivism in turn leads directly to egoism, i.e. the belief that one should put one's own interests ahead of the interests of others, and egoism leads ineluctably to the ethic of "might makes right".
Hitler's "morality" was completely consistent with his rejection of a belief in a transcendent moral authority, a God.
Indeed, Hitler was what every atheist would be if a) he or she had the power Hitler had and b) he or she were logically consistent.
Thankfully, few of those who reject belief in a transcendent moral authority are both powerful and consistent, but in the 20th century some were. Mao, Stalin, Pol Pot and Hitler all were atheists who had complete power within their sphere and acted consistently with their naturalistic, materialistic worldview. The horrific consequences were completely predictable.