D. A. Carson on the legacy of secularism in the twentieth century:
The twentieth century, the bloodiest in human history, exhibited spectacular instances of intolerance—and the most violent exemplars had very little to do with religion. Of course, there was at least a religious component in the strife in the Balkans and again in the bloody violence between the Tutsis and Hutus. Yet most observers recognized that even here the more important factors were tribalism, racism, perceived economic injustice, very different interpretations of history, and "honor" and vengeance killings that escalated to the scale of genocide.
Few religious factors played much part in the largest of the slaughters of the twentieth century, the violence espoused by Fascism and Communism. Perhaps fifty million Chinese died under Mao, about twenty million Ukrainians under Stalin, and then we come to World War II and the Holocaust. In both its Russian and its Chinese forms, Communism was overtly atheistic. In both its German and its Italian forms, Fascism was nominally Christian but only in the sense that it was happy to appeal to God and religion in pursuit of its own social and political agendas, never so as to be reformed by Scripture or Christian truth or morality, never in any sense to belong to the great tradition of historic creeds. . . . Atheism, whether theoretical (as in Communism) or practical (as in Fascism), far from being tolerant, spilled oceans of blood.—D. A. Carson, The Intolerance of Tolerance (Grand Rapids: Eerdmans, 2012), 72-73.