Here is what Toronto is not: Toronto is not dirty, dangerous, or poor. Toronto is not a hell of lost liberties or a babble of cultural incoherence or a ruin of failed institutions. Yet a popular argument against high levels of immigration suggests it should be.

In his 2004 book Who Are We?: The Challenges to America's National Identity, the late Harvard political scientist Samuel Huntington warned that "the United States of America will suffer the fate of Sparta and Rome," should its founding Anglo-Protestant culture continue to wane. Commenting sympathetically on Huntington's argument, conservative writer John O'Sullivan asserts that if traditional patterns of national life are "removed or destroyed, then anomie, despair, and disintegration tend to be among the consequences." So we must take care to protect our precious cultural patrimony from the acid of "denationalizing" economic and cultural globalization. We must keep outsiders out.

Successful societies (so this argument goes) owe their liberty and prosperity to distinct institutions which, in turn, depend on the persistence and dominance of the culture that established and nurtured them. Should that culture fade—or become too diluted by the customs, religions, and tongues of outsiders—the foundation of all that is best and most attractive about that society cannot long last.

But somebody forgot to tell Toronto! Nearly half the denizens of Canada's most populous metropolis were born outside the nation's borders—47 percent according to the 2006 census, and the number is rising. This makes Toronto, the fifth biggest city in North America, also the most diverse city in North America. Neither Miami, nor Los Angeles, nor New York City can compete with Toronto's cosmopolitan credentials.

Here is what Toronto is: the fifth most livable city in the world. So said the Economist Intelligence Unit in a report last year drawing on indicators of stability, health care, culture, environment, education, and infrastructure. (The Economist's world champion of livability, Vancouver, harbors a treacherous 40 percent foreign-born population.) Toronto is wealthy, healthy, well-educated, and much safer than any sizable American city. In 2006, its murder rate was 2.6 per 100,000 residents, which makes it less than half as deadly as Des Moines. The most culturally mixed city on the continent truly is one of Earth's closest approximations of urban paradise.

Of course, Canada's legacy of slavery and segregation is far less brutal and defining than is America's. And Canada does not share a long border with a much poorer country, millions of whose people will cross it looking for opportunity no matter what the law says. High levels of low-skilled immigration from Mexico and Central America create real problems in the United States, and Americans are right to worry about them. But these problems have solutions (guest-worker programs, not walls) and imply nothing about the general viability of healthy immigrant-rich societies.

The United States, this fabled land of immigrants, has fallen dismally far behind countries like Australia and Canada in openness to immigration. The Statue of Liberty may as well be moved to Vancouver's English Bay where the "huddled masses yearning to breathe free" are now rather more welcome than in New York Harbor. Many Americans, convinced by arguments like Samuel Huntington's, have come to believe that the institutions we so rightly cherish are too dependent on a feeble, endangered cultural inheritance to survive the bustling presence of strange languages, exotic gods, and pungent foods. That cultural fragility argument is false, and it deserves to die.

Toronto, which has an Anglo-Protestant heritage as strong as any, has proved it dead wrong. In fact, Toronto shows that a community and its core institutions can not only survive a massive and growing immigrant population but thrive with one. Multicultural Toronto and cities like it prove that the institutions of liberal modernity are robust. Life within them is so good that people the world over flock to them. And newcomers do not take these institutions for granted. They have a stake in seeing them last. They can and do make them stronger.

None of this is to say that Toronto doesn't have its problems. (Or that it’s not boring to New Yorkers.) But we would do well to learn the lessons of cultural accommodation and integration from our neighbors to the north. American cities could host much larger immigrant populations and thrive. Maybe someday an American city will place in the top 10 on the list of the world's most livable places. Maybe—if it becomes more like Toronto.