Jonah Goldberg once wrote a book about the “tyranny of cliches.” Perhaps that’s why he takes a special interest in the oft-cited notion that America’s strength is based on its diversity. National Review Online readers benefit from Goldberg’s insights.

Senator Lindsey Graham (R., S.C.) says he scolded the president for saying something scatological about certain countries and their emigrants. “Diversity has always been our strength,” Graham allegedly said. By my very rough count, this makes Graham the bazillionth person to proclaim some variant of “diversity is strength.”

But is it true? I think the only close to right answer is, “It depends.” Specifically, it depends on which (often clichéd) analogy you want to hang your argument on. Diverse stock portfolios are more resilient. Diverse diets are healthier. But that doesn’t mean picking bad stocks will make you richer, nor that eating spoiled foods is good for you.

I once heard the Reverend Jesse Jackson explain that racial integration of the NBA made it stronger and better. He was right. But would gender integration of the NBA have the same effect? Would diversifying professional basketball by height? Probably not.

In other words, all of these analogies can only take you so far. Thomas Sowell once said, “The next time some academics tell you how important diversity is, ask how many Republicans there are in their sociology department.”

There’s a growing body of evidence that even if diversity once made America stronger, it may not be doing so anymore, at least in the short and medium term. Robert Putnam, a liberal sociologist at Harvard, found that increased diversity corrodes civil society by eroding shared values, customs, and institutions. People tend to “hunker down” and retreat from civil society.

I think the real culprit here isn’t immigration or diversity in general, but the rising stigma against assimilation.