In short, most racism is coming forth from unfamiliarity.
This is just a meaningless PC slogan. It has no value whatsoever. In fact a lot of people become racists when they come to know others better and decide the others, their culture, habits and values are undesirable. How would Christians like polygamy accepted by Islam?
So would you say the reason for slavery was that people were unfamiliar with those they enslaved? Were Jews newcomers to Germany just a few days before Kristalnacht? Did Germans kill Jews because they didn't know enough about them?
IMO racism is a natural biological tendency and it has been a part of human evolution. Hence we have... human races. We tend to organize ourselves into various groups, sports teams, hobby clubs, linguistic groups, nations and countries. Sometimes racism will manifest itself as unwillingness to be close to the others, sometimes it will take more drastic forms.
Saying that young children playing together and without regards to racial differences has a meaning for racial debates is like saying that combing one's hair is unnatural because babies are born bald, and speaking should be banned because babies cannot speak either.
A lot of physical and psychological qualities in a human being are a matter of the stage of life. Children are born with some qualities that vanish, and they acquire other qualities as they grow up and age. Anybody who has even a faint idea of human developmental psychology will know that.
Some say that racism is whatever-phobia. Yes it is. One of the most powerful driving forces in biology is fear. Its function is survival. That's why we eat (we don't want to die of hunger) or withdraw out hand when it's exposed to fire (we don't want our hand to be burnt). That survival instinct extends to entire groups of people, with division spanning and crossing various lines. And it is also true when it comes to things such as skin color, family tradition etc. The tendency has been to preserve some of the defining qualities of various groups. That's why white people have been killed by non-white natives around the world, and that's why whites killed even more non-whites.
Btw. do gays fight for sexual rights of the straight people? Such as the right to be free from exposure to homosexual exhibitionism?