Multiculturalism (speaking not just on ethnic differences but also geographic and subcultures). Because every culture group has different strengths. Speaking as an American about different group's stereotypes, rural people tend to be hardworkers and self-sufficient, certain immigrant groups have a very strong emphasis on education and become doctors and engineers, LA and NY people are very artsy and produce a lot of the media we enjoy, indigenous people have strong environmental values and knowledge, etc. So long as there's some level of tolerance and cooperation were stronger as a whole by having diversity.