It is human nature to be afraid of things that are different. From the beginning of time all races have tried to subjugate the ones that have different color skin, speak a different language, or have a different culture. Look at the Old British Empire and the rise of Colonial America. Both were founded on the more technologically advanced race deciding they were superior and conquering the weaker races (India, Native Americans, etc...)
Humans will always have a fear of that which is different from what they know, but I think that as a species we are becoming more and more accepting of differences, so long as they aren't deemed evil by us, like slavery is.