diversity is a strength?

can someone explain to me how diversity is a "strength"? what exactly is the benefit of mixing people of random languages, religions, ancestries, eye colors, hair colors, height, intelligence, and class in a small localized area?

differences in people are the number one cause of war. end the hate. separate.

Mismatched alleles in mulattoes can lead to autoimmune diseases, such as arthritis and multiple sclerosis, where the immune system inherited from one parent attacks the proteins made from the other parent’s DNA. Ness, 2004. There are rearrangements, inversions, and duplications in the human genome that differ among the races and may cause incompatibility. There are also some non-genetic costs of race-mixing, such as cultural incompatibility and the spread of a disease that one of the parent populations is immune to but the other is not.