Racism has had no real positive effects in history, dear. Take it from a historian.
We probably are hardwired for it to some extent, since it would have offered our ancient ancestors some survival advantages. In our early history, we needed to be suspicious of and even hostile towards the Other -- the person who didn't look like us and didn't share our customs and beliefs -- because life was tough then, and chances were that he didn't want to be friends; he just wanted what we had.
But we're not Stone Age people, or even living in the Bronze or Iron Age. We have presumably progressed a great deal, and as I said, in mankind's recent history, racism hasn't had any positive effects on culture and civilization. It is no longer "rational" to be racist.
Multicultural civilizations, by the way, are always richer, deeper, and more sophisticated than others. Cultural homogeneity is narrow, restricted, and impoverished.