I think the reason people have had the historical tendency to view those different than them as being legitimate objects of ridicule (and worse) is because historically, the majority of peoples' worlds were very, very small. Before mass communication, like radio, TV, and now, the internet, people were usually only exposed to those who were in their immediate surroundings, who were usually very much like them culturally, as well as ethnically.

The new technologies that have changed all of that for people in the industrialized part of the world (and also in some parts of the developing world), have only been available to the masses for less than a century, and in the case of the internet, for a couple of decades. I think attitudes have changed a hell of a lot in such a short period of time, and I think it's because peoples' worlds are getting much bigger, people are now much more accustomed to seeing people who are different then they are as a normal part of their environment, and because people have more opportunities to form bonds with people from other cultures and ethnic groups. On the internet, for instance, people can form very significant bonds with people they've never met, and often times, don't even know what their ethnic group/culture/race is.

Young people, especially, are disinclined to be bound by old notions about appropriate attitudes and behavior towards those who are different than they are. To adhere to old attitudes limits their world, and their choices, and that is very unappealing to most of today's young.