The confusion of diversity and multiculturalism.

I'm going to separate the myth of multiculturalism being for the benefits of diversity, arguing the two aspects of diversity, Genetics and Culture, then I will breach upon intent and politics.

Oh, I decided this will be in a couple of parts, this one will just be genetics.

Despite our large population and world wide distribution, humans are genetically less diverse when compared with other mammalian species, not only that but ~85% of genetic variation exists within populations, 5%-6% distributed between localized populations within the same continent and only 6%–10% between large groups living on different continents, genetic diversity brought by immigration is minimal, but if you're still convinced, emigrating to Africa is the best course of action, as African populations contain 100% of human genetic diversity, while populations further away, such as the population of New Guinea, contain only ~70%. Massive, exponential immigration are nowhere needed to prevent any symptoms of inbreeding depression.

Darker skin appears to be strongly selected for in equatorial regions to prevent sunburn, skin cancer, the photolysis of folate, and damage to sweat glands; lighter skin allows the body to form greater amount of Vitamin D which helps prevent rickets. Similar skin color in different races occur from convergent adaptation, not genetic relatedness, the similarity in skin pigmentation within certain populations is also likely due to sexual selection.

The categorization of racial groups is false in many areas and because most variation is within group, categorizations are not necessary, nor are they absolute. The diversity is not through actual genetics, but through what is perceived.

Now, assuming most of this is false, what would the forced admixture bring but the homogeneity of all races? If isolated groups were to mix with larger races, the existence of the isolated group would disappear after a few generations, like the Tasmanian Aborignes. If one were to keep the diversity, groups would have to be partially exclusive, and this is exactly what happens, people keep to their own, with a small ratio of interbreeding.

Now that's done, I can get into the real argument.