What I find paradoxical with the believe that homogeneity encourages strength, better innovation [which, by all research, is statistically positive], culture is that those supposedly homogeneous 'tribes' or 'realms' were created by the very suspicions of others who look just like them to begin with. Going back hundreds, to hundreds of thousands of years. What I find fascinating with people is how they look at things through a modern lens [say the past hundred or so small years].

I think this also leads to the whole correlation / causation thingamajig. Just because historically homogeneity means closer cultural comfort, closeness, etc. doesn't mean that it will always be so. there's so much confounding factors and a multitude of variables that could've easily swung in and out of a group's favor down the line.

It's also dually possible that in the far, far future you can have a multi-ethnic, uni-cultural world of sorts. like Star Trek. cue: 'but human nature!!1'. Yeah. people will always form tribes..it's not just limited to race.