However great the shock of the massacre in Orlando, it is only a matter of time before we start hearing again the fact-free dogma that “diversity is our strength.”

If there is any place in the Guinness Book of World Records for words repeated the most often, over the most years, without one speck of evidence, “diversity” should be a prime candidate.

Is diversity our strength? Or anybody’s strength, anywhere in the world? Does Japan’s homogeneous population cause the Japanese to suffer? Have the Balkans been blessed by their heterogeneity — or does the very word “Balkanization” remind us of centuries of strife, bloodshed and unspeakable atrocities, extending into our own times?

Has Europe become a safer place after importing vast numbers of people from the Middle East, with cultures hostile to the fundamental values of Western civilization?

“When in Rome do as the Romans do” was once a common saying. Today, after generations in the West have been indoctrinated with the rhetoric of multiculturalism, the borders of Western nations on both sides of the Atlantic have been thrown open to people who think it is their prerogative to come as refugees and tell the Romans what to do — and to assault those who don’t knuckle under to foreign religious standards.

The recent wave of refugees flooding into Europe include Muslim men who have been haranguing European women on the streets for not dressing modestly enough, not to mention their sexual molestation of those women.

Smug elites in Europe, like their counterparts in America, are not nearly as concerned about such things as they are about preventing “Islamophobia.” Legal restrictions on free speech in some European countries make it a crime to sound the alarm about the dangers to the culture and to the people.

In the lofty circles of those who see themselves as citizens of the world, it is considered unworthy, if not hateful, to insist on living according to your own Western values or to resist importing people who increase your chances of being killed.

But if you don’t have the instinct for self-preservation, it will not matter much in the long run whatever else you may have.

America’s great good fortune in the past has been that Americans have been able to unite as Americans against every enemy, despite our own internal differences and struggles. Black and white, Jew and Gentile, have fought and died for this country in every war.

It has not been our diversity, but our ability to overcome the problems inherent in diversity, and to act together as Americans, that has been our strength.

In both World War I and World War II, the top commander of American troops who went into combat against the German army was of German ancestry — Pershing and Eisenhower, respectively. So too was General Carl Spaatz, whose bombers reduced German cities to rubble. Whatever their backgrounds, they were Americans when the chips were down.

Today, that sense of American unity is being undermined by the reckless polarization of group identity politics. That affects not only how Americans see themselves, but how others in our midst see America.

Some people demand American citizenship, as if it is an entitlement, while burning the American flag and waving the flag of Mexico. And the apostles of “diversity” and “multiculturalism” watch in silence. That includes the President of the United States.

Probably most people in most groups are decent. But if 85 percent of the people in Group A present no serious problems and 95 percent of the people in Group B present no serious problems, that means you can expect three times as many serious problems when you admit immigrants from Group A.

Unfortunately, there is remarkably little interest in the relevant facts about crime rates, disease rates, welfare dependency or educational deficiencies among immigrants from specific countries. Most debates about immigration policies are contests in rhetoric, with hard facts being ignored as if they didn’t exist.

Tragically, the massacre in Orlando seems unlikely to change that. Too many people have too much invested in their own particular position to change, especially in an election year.