The opposite of diversity is not coherent, it is myopia. Groups lacking diversity lack fresh insight and allow opportunities for stereotype and intolerance to grow. I've encountered exactly this in dozens of Midwestern suburbs. I grew up in a town and school district where our class had "the black kid", "the Latino kid", "the Vietnamese girl" and so on surrounded by hundreds of white kids. The misinformation was real, and the opportunity to talk to someone and dispel those beliefs was low. University offered a chance to fix some of that, but my former classmates who never left town are bye and large a bunch of bigots. On the other hand, people I knew who were raised in diverse areas learned much broader perspectives and manage to incorporate new view points more easily.
We are programmers yes? Is a monolith better or is mass distribution better? Depends yes?
In business and operations do economies of scale exist? Or is it always better to be separate individual groups not operating under a larger shared structure? Depends.
"Diversity" taken to the extreme is entropy. Obviously extreme entropy is incoherent.
Politically, socially, culturally, mass diversity is correlated with decline of social cohesion, loyalty, trust, common sacrifice and rise in tribal and political conflict.
There are advantages for sure to exposure to broad viewpoints and new information. Having a cohesive and generally homogeneous society (and this can be defined along many axes don't forget.. not just "race". How about social values, political views, ethnic culture, shared historical experience etc) does not preclude one from learning and being curious and open to new perspectives. But it does eliminate petty conflicts that can waste time and energy and get in the way of real progress and collective power.
When you hear about companies strongly promoting their "company culture", aside from the requisite amount of skepticism about this being marketing and hot air, is there a kernel of truth to the idea that everyone being on some degree of the same page helps that organization work together better to achieve shared goals?
Would it be better for, say, a military unit, a sports team, a corporation to have all their members having very divergent viewpoints, cultural values, philosophies, mission statements, purposes, motivations etc? Not always. Can we at least say that... not always?
Team building, creating elements of homogeneity, shared purpose, and loyalty, wouldn't be a common endeavor (not that it is perfect) for all of these entities if so.
>and so on surrounded by hundreds of white kids
I absolutely agree that life is harder for a minority amongst a divergent majority. This is possibly an argument against putting people in this situation. Is it better for them? Your statements sound like it is not.
