Racism is just a prejudice. Someone who is racist is no lower than the next person. Racism is just one of those prejudices that are considered 'politically incorrect,' so of course a majority of society is going to frown upon it to avoid being tagged a social outcast. Your prejudice against the heavy-set lady across the street is no better than your fathers prejudice against Koreans. The preachers prejudice against sinners is no better than the poor mans prejudice against bankers. And the environmentalists prejudice against lumberjack's is no better than the American governments prejudice against communism.
The question should not be "Why are some people prejudice?", but, "How many prejudices?" Most are even prejudiced against the word prejudice because they are taught that it is 'politically incorrect.' A great man once taught me about the 'cluster concept.' "People's personalities, their likes and dislikes, their attidues, and viewpoints, their prejudices come in clusters, as grapes come in bunches. If you examine one grape you will know pretty much what the rest of the grapes on the cluster look like. If you taste one you know how the others will taste. There may be minute defferences from grape to grape, but you can bet that the grape you didn't taste does not taste like beefsteak." The word prejudice, pretty much to me, is based on the 'cluster concept.'
In the world we live in today, it is pretty much impossible not be prejudice against something. Prejudice, by itself, is just another imperfection of the human race.