Surprisingly enough I thought a New York Times editorial on the movie "The Help" was really excellent. It addresses the fact that the characters displaying racism and otherwise negative traits are almost always generally despicable people. Rarely are these people portrayed as good people who also happen to have these traits.
This is a major problem with understanding these issues and is not limited to racism. There is a big difference between social and individual evil. We deal very well with individual evil, most things we consider individually evil are carried out with intent to cause harm and are easily categorized.
Social evil is very different. All social evil has its roots in people's desire to do good. Even concepts such as racism were grounded in people's deep beliefs in how to create a morally ordered society and the people engaging in these behaviors usually had the best of intentions. This goes especially for the great 20th century evils, Hitler, Stalin, Mao, and Pol Pot all had ideas about what was best for their societies and lived in and created cultures that attempted to fulfill their moral vision. Going back further in history, the Inquisition, witch burnings, and even the Mongol invasions require knowing that these were perceived by the actors involved as being measures to protect and benefit their societies (though in individual cases individual aggrandizement was certainly a factor but this aggrandizement could only be exercised because of a social and cultural consensus regarding the basic rightness of the act).
The evil of these things is rarely seen at the time by those that share the perpetrator's culture, in most cases, the belief in the rightness of these acts are widely shared. It is only outsiders, whether those from another culture or future observers, that can properly judge the morality of social norms and customs. We should be very, very sceptical of any claims of ability to change society on a social or moral level. Thus far, all experiments of this type have ended badly, whether social engineering, massive economic restructuring, or conformity to rigid religious beliefs.