Just completing a two-week tour of poverty in the United States, Philip Alston offered an assessment that was by turns sobering and alarming. Essentially alone among its peer states in the West, the United States, despite its wealth and advanced technology, has maintained a policy of prolonged indifference to conditions of poverty that is thwarting the advancement of millions of its citizens.

Infant mortality in the United States is “the highest in the developed world,” and, owing to inadequate sanitation, “neglected tropical diseases are making a comeback,” Mr. Alston said. Because of its failure to provide universal health care and its market-driven model of health care delivery, “Americans can expect to live sicker and shorter lives,” he said, than the citizens of any other advanced economy. Youth poverty in the United States is the highest among the nations of the Organization for Economic Co-operation and Development, “the rich countries’ club,” he added, and “the United States ranks 35 out of 37 in the O.E.C.D. in terms of poverty and inequality.”

Sometimes an outsider’s perspective can be helpful for a clear-eyed evaluation of a society’s weaknesses. Mr. Alston, an Australian, is the special rapporteur on extreme poverty and human rights for the U.N. Human Rights Office of the High Commissioner. “At the invitation of the federal government,” he said in a summary of the mission report, he had been asked to look at whether “the persistence of extreme poverty in America undermines the enjoyment of human rights by its citizens.” He reviewed the results of his investigation with the press in Washington on Dec. 15.

The United States is thwarting the advancement of millions of its citizens, a UN rapporteur says.

According to the most recent statistics from the U.S. Census Bureau, more than 40 million people—more than one in eight Americans—are living in poverty. Almost half of those, 18.5 million, are living in deep poverty, with reported family income below half of the poverty threshold.

At the beginning of December, Alston’s U.N. team began a nationwide fact-finding mission, visiting pockets of poverty around the country in Alabama, California, Puerto Rico and West Virginia. Mr. Alston and his investigators spoke with local political and civic leaders about the conditions of U.S. poverty and the efficacy of anti-poverty efforts. Much of what he encountered came as a personal shock, he said, measured against the overall wealth of American society.

People in the United States often speak of its egalitarianism and American exceptionalism. They take pride in “the American dream,” he said. But, he warned, “a child who is born into poverty has almost no chance to move out of poverty in the United States today.”

More than 40 million people—more than one in eight Americans—are living in poverty.

He encountered social conditions because of poverty that cannot be found in other advanced economies of the world, he said. Mr. Alston, surprised to discover that “hookworm in the 21st century” was a significant problem in the United States, marveled at a related phenomenon: the percentage of U.S. households that were responsible for maintaining their own water supplies and septic systems, as if ensuring safe water and sanitation were not an obligation of government.

Though poverty rates have remained mired in the low teens for decades, Mr. Alston acknowledged that his U.N. mission had been called at an especially dramatic moment in U.S. political life. Not far from the site of his press conference, final discussions were taking place on a tax plan that could ultimately mean, U.S. bishops have warned, greater burdens on the poor through additional taxes and social service cuts even as it directs more wealth into the hands of the nation’s richest people.

“For a country able to transfer a trillion dollars to its wealthiest not to be talking about taking care of basic health needs is stunning,” he said, arguing that the struggle to access adequate health care had become a crushing burden on U.S. poor—one not experienced by low-income individuals of many other societies.

According to international law, he said, “every person has the right to an adequate standard of living and where that seems impossible, it is the role of government to assist them.” A significant challenge to human rights in the United States emerges out of the problem of those unaddressed needs. “I believe that current trends in the United States are actually undermining democracy,” Mr. Alston said. “What we see are the lowest voter turnouts in any developed country; we see overt efforts to disenfranchise people.”

Ultimately the poor in the United States, he warned, are unable to significantly contribute to the political process or influence the policies that affect their lives. A criminalization of poverty through civil fines and penalties and harassment of the homeless, he argued, further exacerbates their disenfranchisement, as do more covert efforts like voter ID laws and the closing of voting facilities in low-income communities.

The poor in the United States, he said, could easily be able to lead lives with dignity if minimal social commitments were met. “Surely it’s the obligation of a society to ensure basic goods,” he said, pointing out that the poor in America also struggle to get dental care and access mental health services, two other major obstacles to finding the jobs that could lift them out of poverty.

The poor in the United States could easily be able to lead lives with dignity if minimal social commitments were met.

Many of the homeless he met, he said, were suffering from mental health problems or were U.S. veterans struggling in the aftermath of their service. “In a country like the United States, homelessness could be eliminated pretty quickly.” It is not, he said, because Americans simply “don’t want to put the money into it.”

“What I have seen in the United States is the dominance of twin narratives,” he said, one depicting the wealthy as productive, hardworking and altruistic, and the other purporting the poor as “losers, scammers, people attempting to profit from the system.”

The narratives, which are also complicated by racism, he said, are used by politicians “to rationalize massive tax cuts for the richest and massive cuts in the basic assistances that are made available to the poor.”

In his report, Mr. Alston said, he also “saw much that is positive.” Meeting with state and especially municipal officials “who are determined to improve social protection for the poorest 20 percent of their communities,” he saw “an energized civil society in many places.”

“I visited a Catholic Church in San Francisco [St. Boniface, which hosts the Gubbio Project] that opens its pews to the homeless every day between services; I saw extraordinary resilience and community solidarity in Puerto Rico; I toured an amazing community health initiative in Charleston [in West Virginia] that serves 21,000 patients with free medical, dental, pharmaceutical and other services.”

But such community-based efforts, despite their energy and good intentions, are not enough to contend with larger social forces. In the report’s summary, Mr. Alston argues, “Successive administrations, including the present one, have determinedly rejected the idea that economic and social rights are full-fledged human rights, despite their clear recognition not only in key treaties that the U.S. has ratified…[but also] in the Universal Declaration of Human Rights which the U.S. has long insisted other countries must respect.

“But denial does not eliminate responsibility, nor does it negate obligations,” he writes. International human rights law “recognizes a right to education, a right to healthcare, a right to social protection for those in need, and a right to an adequate standard of living.

“In practice, the United States is alone among developed countries in insisting that while human rights are of fundamental importance,” he continues, “they do not include rights that guard against dying of hunger, dying from a lack of access to affordable healthcare, or growing up in a context of total deprivation.”

Kevin Clarke is America’s chief correspondent and the author of Oscar Romero: Love Must Win Out (Liturgical Press).