> To value diversity of ethnicity or race, you must believe there are intrinsic differences between people which are determined by their ethnicity.
I think that's easily proven false. I value diversity of ethnicity and race because I think it's statistically more likely that it results in diversity of culture, and I think that's the real useful thing to be aiming for.
In the United States "white" isn't a race any more than "black" is. It's a short-hand for a cultural identity that our society foists upon you, and it comes with a mostly shared set of experiences and understanding.
A "black" person (which could be historically from Africa, Asia, South America or elsewhere) will likely face some shared set of experiences, as will a "white" person, or an "asian" person, or a "latino" person. The same could be said for a U.S. citizen or a European.
If you think "white" was used as shorthand for "the largest and most dominant cultural identity in America" as I do, then you think that diversity in that brings different perspectives and cultural norms, and some people find that refreshing and interesting (as well as there being some evidence that it provides many other benefits and detriments to various degrees).
So, do I think skin color is an important determinant of some quality in this discussion? Yes. In the case where you're looking at a mostly homogeneous group based on age and likely cultural identity, I think encouraging differences in both age and that cultural identity are likely to introduce more cultural diversity than some other options, and that's based on sociological and statistical beliefs. You may or may not think that qualifies as racism, but I don't, and part of that is because I don't think the result is based on actual skin color, just skin color in a geographic region (that is, a country with a different cultural and ethnic makeup may not see similar results). That means skin color is little other than a statistical marker for other, more useful attributes in this case.