This week the world will observe the 60th anniversary of the liberation of Auschwitz, the concentration camp that claimed nearly a third of the six million Jews murdered by the Nazis. In his harrowing memoir of survival, Night, Elie Wiesel asks: "How could it be possible for them to burn people, children, and for the world to keep silent?"

There can be only partial answers to that question, but certain facts surely contributed to the silence, especially in the United States. Throughout the 1930s, most Americans wanted nothing to do with another European war. Despite mounting evidence of Hitler's barbarism -- and his ultimate military aims -- the mood was stubbornly isolationist. This was particularly true of the nation's religious leaders, who were preoccupied with America's economic and social injustices.

Some saw German aggression as a kind of divine judgment. "Our sins have found us, that's all," explained John Haynes Holmes, pastor of New York City's Community Church. "If Hitler triumphs, it will be as the punishment of our transgressions." A.J. Muste, a Congregationalist minister turned peace activist, compared pro-democracy hawks to "the men who tortured and killed the victims of the Inquisition." Albert Palmer, president of Chicago Theological Seminary, said Americans should be "solving the problems of social and economic justice" at home rather than condemning Germany "through a haze of Allied propaganda."

The Christian Century magazine, the nation's leading religious journal, devoted itself to opposing U.S. intervention. Writing as late as November 1941, editor Charles Clayton Morrison denounced an Anglo-American alliance as "the most ambitious imperialism ever projected." He then offered this dark prediction: "For the United States to make a fateful decision to enter this war on the mistaken and irrational assumption that it is a war for the preservation of anything good in civilization will be the supreme tragedy of our history."

These "progressive" religious thinkers preserved their political and moral neutrality only by downplaying Hitler's anti-Semitic rage. Methodist leader Ernest Fremont Tittle claimed that Nazism could be overcome non-violently -- "with truth and love even unto death" -- yet said almost nothing about the Jewish deaths demanded by his pacifist ideal. When thousands protested the persecution of German Jews during Kristallnacht, Catholic writer Paul Blakely saw only "a fit of national hysteria" orchestrated to drag America into war.

They knew better. The arrests, deportations, and imprisonment of Jews across the continent were widely reported in the American press. Yet the nation's Christian leadership failed even to lobby for immigration reform to absorb more refugees. No wonder: From 1933 to 1941, more than 100 anti-Semitic groups appeared in the United States, many with a Christian hue.

There were other voices. Protestant theologian Reinhold Niebuhr led a group of "Christian realists" who insisted that Hitler be judged not only by his military ambitions, but by the ruthlessness of his anti-Semitism. They accused the isolationists of misusing Christian ethics in order to "drug their conscience" toward Nazi atrocities. "The Christian ideal of love," Niebuhr warned, "has degenerated into a lovelessness which cuts itself off from a sorrowing and suffering world."

At the heart of the realist case for U.S. intervention was a biblical view of human evil and the political duty to restrain it. Reluctance to render ultimate judgments of Nazism, they argued, guaranteed the triumph of a racist ideology and the enslavement or death of millions. "It is important that Christianity should recognize that all historic struggles are struggles between sinful men and not between the righteous and the sinners," Niebuhr wrote after the fall of France. "But it is just as important to save what relative decency and justice the western world still has, against the most demonic tyranny of history."

The temptation to forget that difficult lesson is with us still. Yet it's worth remembering that the Jews were not rescued from Hitler's death camps by obsessing over the failings (or the "imperial hubris") of free nations. Then and now, imperfect democracies are called upon to fight anti-Semitism and all the ideologies of hate -- for they are the only democracies available for the job.

Mr. Loconte is a fellow at the Heritage Foundation and editor of "The End of Illusions: Religious Leaders Confront Hitler's Gathering Storm" (Rowman & Littlefield).