there do exist objective arguments for the pursuit of diversity. there do also exist objective arguments otherwise.

https://onlinelibrary.wiley.com/doi/10.1111/padr.12641

heres an article that discusses how inflated diversity could possibly be a cause of social tension. the article's abstract concludes with a shrug ('too many factors!') but it does provide links to research papers arguing both for and against this case.

on the surface it seems pretty clear to me. behaviour is encoded in genetics. if one were surrounded by the same group for a few thousand years, they would share a common base of encodings, therefore social behaviours could be assumed to a higher degree. reference behavioural encodings drastically diverge across cultures (as embodied by religious value sets, or at a different meta level, the idea of low trust vs. high trust societies). based on this drastic divergence, predictions made about one's neighbour scale downwards in accuracy relative to increased cultural diversity.

so i see that jacking up societal entropy leads to lowered societal cohesion. but thats just my stance and id love to hear yours.