If there is no God, then there can be no objective standards of right and wrong. All we are confronted with is, in Jean-Paul Sartre’s words, the bare, valueless fact of existence. Moral values are either just expressions of personal taste or the by-products of socio-biological evolution and conditioning. In a world without God, who is to say which values are right and which are wrong? Who is to judge that the values of Adolf Hitler are inferior to those of a saint? The concept of morality loses all meaning in a universe without God.
As one contemporary atheistic ethicist points out, “to say that something is wrong because . . . it is forbidden by God, is . . . perfectly understandable to anyone who believes in a law-giving God. But to say that something is wrong . . . even though no God exists to forbid it, is not understandable. . . .” “The concept of moral obligation [is] unintelligible apart from the idea of God. The words remain but their meaning is gone.” (Richard Taylor)
In a world without God, there can be no objective right and wrong, only our culturally and personally relative, subjective judgments. This means that it is impossible to condemn war, oppression, or crime as evil. Nor can one praise brotherhood, equality, and love as good. For in a universe without God, good and evil do not exist—there is only the bare valueless fact of existence, and there is no one to say you are right and I am wrong.
–William Lane Craig, The Absurdity of Life without God
Adolf Hitler worked out an “evolutionary ethic” in Mein Kampf (1924). Applying Darwin’s principle of natural selection of the fittest to human ethnic groups, Hitler concluded that since evolution has produced the superior (Aryan) stock, we must work to preserve it. Likewise he believed that inferior breeds must be weeded out. On this basis he killed six million Jews and about five million other non-Aryans.
–Norman Geisler, Christian Ethics: Contemporary Issues and Options