Why race is a positive thing in society?

Historically, race has not been a positive thing. It has been used to justify the enslavement, segregation, subjugation, and murder of people considered to be in an inferior racial group. Racism has been most evident in the former colonies of Africa, Asia, and Oceania, in the apartheid era of South Africa, and in the Jim Crow era in the United States. Despite the disappearance of de jure or, legal, discrimination in the latter two places, the vestiges of racism remain and are dealt with everyday.
It is important to understand that race is a sociological construct, not a biological one. There are black people, for example, who appear to be white -- and phenotypically, may have mostly European ancestry -- who identify as black and are considered to be so due to the presence of African ancestry. This is due to the lingering "one-drop rule" in the United States which identified anyone with any African ancestry as black, thereby excluding those who could "pass" from the privileges and rights reserved for whites, despite being seemingly "white."
Scientific racism developed in the nineteenth-century. We regard it now as one of the negative manifestations of the Scientific Revolution and the Enlightenment. It used anthropology, particularly the sub-field of physical anthropology, and the pseudo-science, craniometry, which used the measurements of skulls to determine intelligence. The other nineteenth-century pseudo-science, phrenology, which used the measurement of skulls to determine intelligence, character, and talent, would develop out of craniometry.
When we look at how racism has impacted people, we positively regard how creative and strong people became despite seemingly impossible circumstances. When we look today at communities such as any major city's Chinatown or New York City's Harlem, we see them as vibrant, thriving communities that offer a great deal of history and culture. We forget that these communities came into existence because black and Chinese people were not allowed to live anywhere else.
Racism also explains the absence of people of color from certain communities. The city of Tacoma, Washington recently issued an apology for its Chinese Exclusion Act of 1882. The state of Oregon had, for many decades, an active Ku Klux Klan presence, and was advertised to whites out-of-state as a "white utopia" due to its black-exclusion laws which, while not having the legal capacity to keep blacks out, did send the message that they were not welcome. Today, these places are liberal bastions, though sharp income inequality between blacks and whites in Oregon and Washington state persists.
Finally, one can appreciate the cultural innovation that arose out of racial oppression. From former black slaves, we got spirituals, which begot gospel and blues, which begot rock-and-roll and R&B. From the table scraps they were forced to turn into meals, we get "soul food." From the poor blacks and Latinos sequestered into the South Bronx ghetto due to inflation and unemployment, we get hip-hop and all the cultural forms it produced beyond music.
https://www.theatlantic.com/business/archive/2016/07/racist-history-portland/492035/