How alike do people claim to be? The claimed advantage of diversity is that by collecting a sufficiently diverse group, almost always categorized by race or sex, you will obtain a wonderfully multitalented team. This assertion relies on the assumption that there is some particular quality unique to your color or sex.
Do you believe it about yourself? Does anyone?
If you took a group of Spaniards and a group of Russians, both white, and asked them if Russians were the same as Spaniards, what do you suppose they would say? You don't even need to go that far. Here in the US, we find people differentiating Americans and Canadians. How about Ethiopians and Angolans? Are they the same?
The entire edifice of diversity rests on a premise that the proponents don't believe about themselves. The only conclusion I can come to is that the people who believe in diversity are patronizing snobs. While they are unique, you are not. All you little proles out there can be grouped by race or sex. There is nothing about you that makes you sufficiently unique to categorize you any other way.
Maybe diversity happens at the individual level. Of course, if you believed that, there'd be no way for demagogues to garner political power by creating an us vs. them conflict.