Many Americans cling to a belief in comic book villains -- 'Bad Guys' who actually identify with 'Evil'. A few nuts may like to dramatize themselves this way, but the evil they actually manage to accomplish is peanuts compared to what people who think of themselves as 'Good Guys' achieve. The Crusades, the Inquisition, the Holocaust, the slaughters of Protestants by Catholics and vice versa, of Sunnis by Shiites and vice versa, the death squads employed by Latin American dictators -- all these atrocities were committed by people who thought they were ridding the world of evil.
The current Pope thinks atheism is the main source of evil in the world, which is laughable. When Godfroi de Bouillon, the 'heroic' crusader, slaughtered the entire Muslim and Jewish population of Jerusalem, including children and mothers with infants, herding Jews into the synagogue and burning them alive, he called it a "solemn sacrifice to Jesus".
Of course religion isn't the only source of atrocity -- Stalin and Pol Pot demonstrated that non-religious ideologues can hold their own against the religious sort when it comes to crimes against humanity. As Laurens van der Post once said, "Human beings are perhaps never more frightening than when they are convinced beyond doubt that they are right." Blind faith of any kind is the first step toward atrocity.
The real motive behind the flap over Will Smith's remark about Hitler was the deeply embedded need of anxiety-ridden humans to cling to this belief in Good Guys and Bad Guys. Smith merely observed that Hitler didn't go around saying "I'm going to do something evil today", but thought of himself as doing good. Of course he did. As do the overwhelming majority of people who commit atrocities.
Will Smith was deliberately misquoted (as saying "people are basically good", and even that "Hitler was good") to both ridicule him and negate the obvious truth he stated. Americans don't want to face up to the fact that they themselves are capable of atrocity, given the right 'cause' and the encouragement of authorities. They want to believe that they're somehow immune. Dream on. How about "the only good Injun is a dead Injun"? And which was the only nation to drop the atom bomb on a civilian population?
Two things make atrocities inevitable. The first is war. A declaration of war today is a declaration of intent to commit atrocities, for all modern wars involve the mass slaughter of civilians, including children. Our military tries to sanitize this by calling it 'collateral damage', referring to the fact that any time you drop a bomb or fire a shell, or plant a land mine in a populated area, you're going to kill children. But of course with modern weapons you never have to face up to the atrocities you commit. If Truman had ordered our troops to enter Hiroshima and Nagasaki and personally hack to death every man, woman, and child living in them, no one could have denied that it was a crime against humanity. Yet the difference is only that the perpetrators never had to face their victims. (There were probably hundreds of pregnant women killed in Hiroshima and Nagasaki, by the way, but right-to-lifers don't seem to be concerned about fetuses extinguished by war. After all, in the Bible the Israelites often slaughtered the inhabitants of entire villages, including pregnant women, supposedly on orders from God, which, I guess, makes it O.K.)
The second inevitable source of atrocity is the concentration of power into too few hands. People have always felt free to commit every conceivable brutality if their king, dictator, Pope, or Imam has told them their enemies were evil, or less than human. It's virtually impossible to find a major atrocity in history that didn't have the explicit support or implicit permission of some authoritarian leader. Power automatically corrupts, sooner or later, without exception; and the more concentrated it is, the more evil it tends to produce. We don't have to look far for contemporary examples.