If you want to understand the Left, most of what you need to know can be summarized thus: The Left hates inequality, not evil. As one raised as a New York Jew (who, moreover, attended an Ivy League university) and therefore liberal -- it took me a while to recognize this fatal moral characteristic of the Left. But the moment I realized it, it became immoral not to oppose leftist values. It is neither possible nor virtuous to be devoid of hatred. Even those who think it is always wrong to hate must hate hatred. The question therefore is not whether one hates but what (or whom) one hates. For example, on the basis of the value system that I hold -- the Judeo-Christian -- I try to confine my hating to evil. By evil I mean the deliberate infliction of unjust suffering on the undeserving; cruelty is the best example of such evil. Those who hate evil hated the Soviet Union. The Soviet Union, after all, was a made-up country, created by a band of gangsters called Bolsheviks and Communists. They murdered between 20 million and 40 million innocent people, spread their totalitarianism around the world, and thereby rendered hundreds of millions of people slaves and automatons. From the 1930s to the 1950s, liberals and social democrats vigorously opposed communism. But the rest of the world's Left, especially its intellectuals and artists, not only did not oppose communist governments, they were the greatest defenders of communism. By the end of the Vietnam War (begun and prosecuted by liberals), however, most liberals abandoned anti-tyranny, anti-evil liberalism and joined the rest of the Left. Since the late 1960s, with almost very few exceptions (one is Sen. Joseph Lieberman), "liberal" and "Left" have become synonyms. (That is why The New York Times characterizes the Nation, a far-left journal, as "liberal.") Thus, when President Ronald Reagan called the Soviet Union an "evil empire," the liberal world condemned him. The Cold War, once regarded as an epochal battle between freedom and tyranny, came to be regarded by liberals as an amoral battle between "two superpowers." Likewise liberals almost universally mocked President George W. Bush when he labeled Saddam Hussein's Iraq, North Korea and Iran an "axis of evil." It takes a mind that either has little comprehension of evil or little desire to confront it to object to characterizing three of the worst regimes in modern history as "evil." How else can one explain the Left's enchantment with Fidel Castro, the totalitarian ruler of Cuba? Clearly his evil is of little consequence. What matters to people on the Left is that there is free health care and almost universal literacy in Cuba. Whereas non-leftists believe that it is far better to be illiterate but free, leftists believe that it is better to be a literate slave. Today, this inability to either recognize or to hate evil is manifested in the liberal opposition to the war in Iraq. As I pointed out in a previous column, opponents of the war should be asked to at least acknowledge that America is fighting evil people and an evil doctrine in Iraq. But even that is difficult, if not impossible, for most people on the Left. As noted above, everyone hates someone, and that includes people on the Left. The problem is that because they don't hate evil, they hate those who oppose evil. That is how liberals went from anti-communist to anti-anti-communist. To paraphrase one of the greatest moral insights of the Talmud, those who show mercy to the cruel will be cruel to the merciful. So, George W. Bush, not the Islamic terror world, is the Left's villain; life-embracing Israel is the Left's villain, not their death-loving enemies; and religious Christians who note moral weaknesses within the Islamic world are the real danger, not the moral weaknesses within the Islamic world. To be fair, it should be noted that confusion over evil and insufficiently hating it are not confined to the Left. There are religious people who conflate sexual sin with evil and/or advocate automatic forgiveness of all evildoers, even when no repentance has taken place. But the inability to acknowledge the greatest evils, let alone to join in fighting them, is the defining characteristic of the Left. That is why former Vice President Al Gore just announced that global warming was a worse threat to humanity than terrorism. He really believes that. As do the great many people on the Left whose moral passion focuses more on gasoline prices, drug prices, health care prices, and other expressions of material inequality than on people and movements dedicated to murder. That is why Robert Redford and friends from Hollywood can celebrate Fidel Castro. Castro may imprison political opponents, and most Cubans may have no right of dissent, but they are economically equal. Dennis Prager is a radio talk show host, author, and contributing columnist for Townhall.com.