Not everyone thinks racism is wrong.
Not to mention it isn't always to do with seeing someone who has a different skin colour to you and hating them. A lot of people dislike/judge the ways of certain cultures/religions which are subsequently followed by a certain race. So they dislike the race.
Ideally we would all happily be friends regardless of ethnicity but I think often cultural issues come into play. And culture and race are often linked. So often people of different races don't really get on with eachother and find common ground, because there are big cultural differences.
Considering how many thousands of years humans have been on the planet, the movements of Martin Luther King etc are still fairly recent.
Ideally, the idea of "race" should be removed from society and we should just see eachother as people. But while there is still so much racial inequality, it isn't possible that we can do this. There's too much emphasis on race in present modern society for there to be no racism, as we still currently aren't at the point where we see people for who they are.
Life is very hard. People tend to look out for themselves. Why would such a dominant race want to give their power away?
Why do people do it?