Call me a cynic, but I believe that, even then, we will find some other distinctions with which to categorize, polarize, and distinguish ourselves from each other. When race is gone, more or less, humanity will still divide itself by some other standard, be it socioeconmics, region, or perhaps even political ideology.
Considering we can't be peaceful within a family of the same race and religion and cultural background, I take that as a given.