Good points. However, the whole "race" aspect is a bit in denial of our potential to unite by recognizing diversity as part of the diversity, variability, and multiplcity that exists int he whole universe. There is no need to deny that there are "races" within the one human "race"/"species", just like it is for nonhuman animals like cats and dogs. The only factors that matter for unity is morality. If a culture or ethnicity isn't morally congruent with another then they can't unite.

Also, seeing this as impossible and that mass civil war would happen, is again predicated on your assumption that you need to deny racial, ethnic and cultural difference sin order to "unite" and would backfire in the ends when people can't deny the reality of the cultural differences they want to live by. The factor that matters is morality.