The greatest barrier to Barack Obama becoming a leader who truly advances the cause of justice is not found in the racially polarizing and unpatriotic comments of his longtime pastor, the Rev. Jeremiah Wright, but in Obama's own vision of civil rights, which cannot be reconciled with the vision Martin Luther King Jr. used to achieve victory for the civil rights movement.

King's vision was as simple as it was unifying: An unjust law is a law that is not consistent with the natural law and the law of God.

The question King put to Americans was: Is racial discrimination consistent with the natural law and the law of God? The question had only one answer: No.

The reason Americans answered correctly is perhaps best explained by St. Paul, who said in his letter to the Romans that all people have the natural law "written on their hearts."

Whether they like it or not, human beings know the basic rules of right and wrong. Great leaders -- like Martin Luther King Jr. -- achieve positive change by forcing people to confront injustice and appealing to what is already written in their hearts to remedy that injustice.

Obama cannot unabashedly embrace this simple vision for a simple reason: He advocates policies that not only violate the natural law, but do so egregiously because they especially victimize children, who because of their vulnerability especially deserve society's protection.

These policies are legalized abortion, which allows unborn children to be killed, and granting same-sex unions the same legal status as marriage, including the "right" to adopt children, which results in children being denied either a mother or a father by the deliberate policy of the state.

Martin Luther King Jr.'s vision derived its political force from at least three factors: It was rooted in a moral tradition that transcends denominational divisions, it was exactly the same vision articulated in the Declaration of Independence, and it was true.

King, an African American Baptist clergyman, explained his vision in the Letter from Birmingham Jail, where he referenced not only the Declaration of Independence, which was drafted by a Deist, but also the writings of two Catholic saints, one of whom died in 430, the other in 1274.

"I would agree with St. Augustine that 'an unjust law is no law at all,'" wrote King. "Now, what is the difference between the two? How does one determine whether a law is just or unjust? A just law is a manmade code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law."

This is precisely what the Founding Fathers were saying when they cited "the Laws of Nature and of Nature's God" and insisted that all men "are endowed by their Creator with certain unalienable rights."

Before the sayings of the Rev. Jeremiah Wright created a national controversy last week, Obama had tipped his hand on where he stood relevant to the Founders' and King's vision of justice.

At a Sunday morning event in Nelsonville, Ohio, earlier this month, for example, he explained why he favors legalized abortion.

He implicitly conceded there is something wrong with abortion, which he said has "a real moral element." But, he concluded, "in the end I think women, in consultation with their pastors, and their doctors, and their family, are in a better position to make these decisions than some bureaucrat in Washington."

That is like saying segregation had a "real moral element" but in end should have been left up to states, local communities and businesses.

On Feb. 28, Obama released an open letter to the "Lesbian, Gay, Bisexual and Transgender" community. "I support the complete repeal of the Defense of Marriage Act," he said. That would mean states would not be protected from having to recognize same-sex marriages codified in Massachusetts or elsewhere.

"As your president," he said, "I will use the bully pulpit to urge states to treat same-sex couples with full equality in their family and adoption laws."

The people who would be bullied by this policy are children who would be thrown -- by edict of the government -- into same-sex unions in which nature itself would never have placed them.

No matter how persistently Obama invokes the rhetoric of national unity and reconciliation, the heart of the country will rebel against the very real consequence that his policies will harm the most vulnerable Americans of all.