Imagine, then, Culture A, with 10,000 enumerable cultural features. Because they are broadly shared by all, nobody is much offended by any of them, and so all of these features can be expressed as naturally in the public square as in the privacy of the home.

Now add a second culture, B, to the Venn diagram. The overlap is close, but not perfect; of the set of 10,000 properties in the first culture’s circle, the second culture shares 9,000 of them. However, because public expression is to be limited to the intersection of the two cultures’ properties, we have now, from the perspective of Culture A, reduced its freedom of public cultural expression by ten percent -- from its full set of 10,000 properties down to 9,000.

Now add a third culture to the mix (and a third circle to the diagram). Because the third culture is distinct from each of the other two, it will, necessarily, further shrink the number of properties common to all three sets -- and thus will further reduce the collection of common beliefs and behaviors that are available for public expression.

This means two things: first, that the more cultures you add to a society the narrower, not broader, the range of public expression becomes; and second, that there will be an ever-increasing disparity between private life (which is now the only place where the full range of cultural life is possible) and public intercourse (which necessarily grows more and more restricted).

Source: The Narrowing Effect Of Diversity – waka waka waka