Im probably going to be the closest one in the thread to agreeing with your friend. However, I see it differently then him.
Basically, I believe he is right in the sense that diversity is “over-rated” in that these days diversity is seemingly being forced upon people/institutions, in that its an issue if something is not diverse enough, when it should not be. Homogeneity does secure and protect culture, however in all honesty the rural farmer from the Midwest does not have anything to worry about because a vast majority of immigrants go to cities for employment. As such, your friend’s argument has value in that statistically there has been more PERSONAL conflict in today’s age due to the way we treat culture, where as in the past these same ethnic conflicts occurred on a national scale (usually colonization related wars). The main issue of cultural conflict is that we expect a “melting pot” (a phrase many in APUSH have heard), and in that we expect people to assimilate into American culture, whatever the current administration deems as American culture, and in that naturally give up some aspects of themselves to do so. Canada, in my opinion, still has these conflicts but to a lesser degree because they talk about diversity as a “mosaic of vast dimensions and great breath”, and as such see everyone as truly separate (a mosaic is a mix of different pieces to make a whole) but equal. As such, diversity is not celebrated, but rather expected to be on its own. The conflicts your friend speaks of are mainly due to the American expectation of melting in, and as such people have difficulty melting in without conflict. Granted, I do think that too much diversity pandering can destroy culture, (just look at Sweden, to me its supposed to be ethnically Swedish people, but all the migrants are slowly eliminating them from their own country).
TLDR: I think OP is right in that more diversity is better for your academic development, but there is such a thing as to much diversity.