re: All of which brings us back the our "ideal" society.
Imagine a world of one racial group, one ethnic group, one language, one set of cultural norms, one economy, one currency, and one goverment. Peace, tranquility, and harmony.
So, who gets to decide which group is the "favored" one? And what happens to the others?
I believe in cultural and racial variety, the interaction of these things, and the resulting syntheses, for the same reason I believe in free markets. A thousand ideas (cultural concepts, genetic patterns, you name it) freely interchanged will give you far better results than one idea (or culture, or race) forced on society by some kind of overlords.
A hybrid cornfield is harmonious and tranquil compared to a rain forest. But only one of these is a robust self-regulating system.