“Can someone relay one concrete example of where diversity has been beneficial without some negative effect?”
No, those on the left are fond of saying “diversity is what made this country great”. Our country is great for many reasons. Our economic system and Constitution has allowed people of diverse backgrounds to work, support their families and thrive despite their diversity. We also had a common language, these immigrants would learn English. Diversity has been used for the last 25 years to divide the population by religion, language, race, nationality, gender, income and now sexual preference, to weaken America and aid the illegal invaders to destroy America the country and ideal.
Diversity does not mean anything except not white male. Although in some contexts it can be expanded to also mean not asian male. You can have a room of 50 black people who all have identical thoughts, and that would be diverse. Ironically, white males are by far a minority on this planet