There have been numerous articles and posts here proclaiming genetic diversity is bad. The referenced study here counters some of those claims. To paraphrase:
After analyzing 102 groups or cohorts covering over 350,000 individuals, researchers have concluded that mixed-race relationships are producing children who are statistically taller and smarter and having a higher level of education. In total, genetic diversity correlated with: "height, forced expiratory lung volume in one second, general cognitive ability and educational attainment." Contrary to popular belief, it doesn't have an impact on medical issues, such as diabetes, high blood pressure, and cholesterol.
Does that mean that non-genetically diverse kids are doomed to be short, fat, and stupid? Of course, not. I'm not. However, statistically, first cousins produce children that are nearly a half inch shorter and have ten months less education. It goes contrary to the idea that homogeneous populations are superior.
I can only speak on one data point--my son. He just turned 3 and is within about a foot of being as tall as my wife. He is well on the way to being in the 95% in height as an adult.
Intelligence is harder to judge at such a young age. He seems to have an aversion to books, preferring to play outdoors and is obsessed with cars. If getting what he wants is a sign of intelligence, he is a master at manipulation.
Beauty is in the eyes of the beholder. Nevertheless, in parts of Asia, mixed-race kids are considered to be more beautiful. My son has already had one serious marriage proposal. It was based on looks and of being of mixed race.
We must conclude that genetic diversity can be a positive. Of course, first, we must accept that being taller, smarter, and having a greater lung capacity are positives for human evolution.