Those who hailed the election of America's first black president, Barack Obama, as evidence that America had progressed to a post-racial society received a cold-water dousing last month in the furor over the arrest of black Harvard scholar Henry Louis Gates Jr. on disorderly conduct charges in his Cambridge, Mass., home.

The incident exposed the fault lines that still persist in our country between white and minority communities. For many blacks, Gates' outburst at police investigating a burglary call at his home was eminently understandable, if not completely justified, by a long history of racial profiling by law enforcement in the United States. For many whites, Gates escalated the situation by seeing racism where there was none, a college professor unfairly claiming victimhood when he was simply being belligerent.

Obama's later-regretted remark at a press conference that the police "acted stupidly" only helped raise the ferocity and longevity of the debate.

Racism and prejudice toward those who are different is as old as human history because it is part of our fallen human nature.

In these enlightened times, few people, outside of the extreme membership of groups like white supremacists, willingly describe themselves as racist. And especially Catholics -- whose coreligionists around the world belong to virtually every race -- know that racism is anathema to the authentic practice of their religion. As the Second Vatican Council, repeated by the Catechism of the Catholic Church, succinctly says: "Every form of social or cultural discrimination in fundamental personal rights on the grounds of sex, race, color, social conditions, language, or religion must be curbed and eradicated as incompatible with God's design."

But race-based prejudice remains much more common than most of us would like to admit. "That racial group is dangerous." "They're lazy." "They exploit their victimhood." "They mooch off society." "I move to the other side of the street when I see one of them coming from the other direction." Or, "they're out to get us."

Recently, our editorial board received an unsigned postcard from a reader in the Pacific Northwest who criticized the choice of photograph for the cover of our Father's Day issue. The photo showed a happy black man carrying his laughing son on his back. "You've caved to black special interests," the reader wrote.

What's certain is that prejudicial attitudes cannot be eradicated by law or even continued close proximity. As Pope Benedict XVI points out in his latest encyclical, the modern push toward globalization "makes us neighbors but does not make us brothers. Reason, by itself, is capable of grasping the equality between men and of giving stability to their civic coexistence, but it cannot establish fraternity."

So what can? Only a lived understanding, the pope says, that each person we encounter throughout the day is, just as much as we are, a son or daughter of God. Our neighbors are much more than nearby households. They are brothers and sisters. Family.

As in any family, we know that members can have real or imagined grievances toward one another. But as in our families, we are called to expand our hearts, offer forgiveness and seek forgiveness, and break down the walls of enmity and hard feelings.

As a quarter of the U.S. population, and with the workings of grace at our fingertips, we Catholics are in a unique position to create an America where not just equality but true fraternity can be the basis of a "post-racial" society.