If there is a silver lining in the fight over Manhattan’s “Ground Zero Mosque,” it is to see that the events of September 11, 2001 remain strong in the public mind. 

Thus it is affirming, in an ironic way, to see partisans on the left and right joining to defend the legal and Constitutional right of Imam Feisal Abdul Rauf to build an Islamic center and mosque at 45 Park Place, two blocks from the perimeter of the former World Trade Center towers.

It will be an irony of a different sort if the $100 million Islamic center rises 13 stories while the new World Trade Center site, nine years after, remains a pit of dust-covered construction struggling to rejoin the life of New York City. For the most extreme elements of Islam, this must seem a crude, enduring victory.

Recall the ringing cries that rebuilding the annihilated 108 stories would be the “best answer” to the terrorists. Absent that, the next-best answer that New York City gave recently was to reassert its belief in freedom of religion and legal title. In an August 3 speech on the Islamic center’s building approvals, New York City Mayor Mike Bloomberg summarized those freedoms as “tolerance.”

One must agree. This is tolerance.

Daniel Henninger says that to reciprocate, Iman Rauf should defend Christian minorities in the Middle East.

Along the way, Mr. Bloomberg noted that denying someone the right to build a house of worship “may happen in other countries” but shouldn’t here. There is a school of thought in this controversy that bringing up the denial of religious practice in “other countries” is irrelevant to discussing the appropriateness of the Ground Zero mosque. I disagree.

Indeed, in the wake of much praise for Mayor Bloomberg’s defense of civil and religious liberty, let me modestly suggest that he next go to Rome in October and deliver a sequel at Pope Benedict XVI’s synod on what the pope recently called the “urgent” plight of Christian minorities in the Middle East. Here, Mr. Bloomberg was preaching to the choir. Try it over there, where it really matters.

We didn’t discover tolerance. Islam coexisted for centuries with Christianity and Judaism. No more. Minorities such as Coptic Christians in Egypt or the Chaldeans and Yazidi in Iraq are being punished or driven out. Churches are destroyed, not built. In April, the Archbishop of Canterbury, Rowan Williams, described the disappearance of Christians from the Middle East as “a possibility that appalls me.” Iran this week sentenced seven Bahá’i leaders, merely for being Bahái’s.

These are national policies, not merely “extremist” Islam. This is directly linked to why the West, including lower Manhattan, is being attacked.

It’s always stirring to see the American Constitution prevail on behalf of unpopular groups, whether neo-Nazis marching in Skokie or Imam Feisal’s Cordoba House in New York. But here’s what’s galling about the Cordoba House affair. There is a sense in which these unpopular causes and people always free-ride on the rest of us who defend freedom. It would be good to see them in return doing their part to keep these principles alive, and that includes Imam Feisal’s unambiguous public support for the embattled Christian minorities in the Middle East.

Islam isn’t just another religion in America. It is bound up in the biggest political struggle of our time. Notwithstanding Imam Feisal’s commitments to “dialogue,” what has he or the rest done to promote and protect the traditions of Western civil society, for which many here and in Europe have fought and died? Maybe the Constitution doesn’t explicitly require it, but where is the good faith on their part?

No institution has spent more time trying to bring Islam toward the modern world’s tradition of civil liberties—that is, the world as we’ve known it for about 250 years—than the Vatican. On behalf of tolerance in the Middle Eastern countries, the Vatican has set up active directorates, sent envoys and held endless symposia on behalf of “understanding” and “dialogue.”

In 1995, the Saudis and others, with the Vatican’s support, opened a large, beautiful mosque in Rome. The expectation was that the Saudis would loosen their restrictions on Christian practice. Despite some one million immigrant Christian workers there, the Saudis have done nothing.

New York City Mayor Michael Bloomberg stands with local religious leaders ..

Frustrated by the repeated failure of Islamic leaders to match promises with practice, Pope Benedict added to the Vatican’s strategy of accommodation a one-word policy, which the tolerance advocates here should adopt: “reciprocity.”

The idea: There will be support for fewer new mosques in the West until the home countries stop hammering non-Islamic religions. Until they reciprocate good will with good will.

Imam Feisal and his partners are getting more than they’ve earned. That’s nice. But even in tolerant America, political life isn’t a one-way street. Islam is in political tension with the world over Islamic terror. The next time a terrorist tries to blow up New York, let’s hope the TV cameras’ first stop for a denunciation won’t be the mayor, but the front steps of Cordoba House.

Write to henninger@wsj.com