Benedict is on his first papal trip to Latin America, where women's rights groups have been pushing to expand access to abortion. With few exceptions, the procedure is illegal in Brazil and most other countries in the region, home to more than half the world's 1.1 billion Catholics.
The pope, who will inaugurate an important regional bishops' conference during his trip, was met at Sao Paulo airport Wednesday by Brazilian President Luiz Inacio Lula da Silva. Speaking in Portuguese, Benedict said he's certain that the bishops will reinforce "the promotion of respect for life from the moment of conception until natural death as an integral requirement of human nature."
Benedict's comments came just hours after one of the president's Cabinet members said a "macho" culture in Brazil has prevented a legitimate debate about legalizing abortion in Latin America's largest nation.
"If men got pregnant, I'm sure this question would have been resolved a long time ago," said Health Minister Jose Gomes Temporao, who is pushing for a referendum on the issue.
Silva recently told a local newspaper that he has always been against abortion personally, but as a president he could not close his eyes from the social problem when the lives of so many women were at stake, reports CBS News Vatican analyst Marco Tosatti.
Silva's spokesman said the president did not intend to bring up abortion during a second scheduled meeting with Benedict.
On Thursday morning, thousands of Brazilians streamed down barricaded streets toward the Pacaembu soccer stadium, where the pope was scheduled to preside over a ceremony for young people.
About 41,000 people were invited, but officials expected at least 100,000 more to gather outside. Not all agreed with the church.
"Until the church broadens its scope of action to include the dispossessed, the poor and the hungry and youth, the evangelical sects are going to continue gaining ground in Brazil," said Charles Marinho de Souza, 27-year-old union activist and member of a Catholic youth group.
Brazil is less and less catholic, adds Tosatti. Only the 64 percent of Brazilian over sixteen years of age declare themselves faithful to Rome. In 1996, before John Paul II last trip to this country, that number was 74 percent.
Even before Benedict got off his plane, he stoked a debate among Catholics who have been arguing whether politicians who approve abortion legislation as well as doctors and nurses who take part in the procedure subject themselves to automatic excommunication under church doctrine.
During the flight from Rome, Benedict gave his first full-fledged news conference since becoming pontiff in 2005. When a reporter pressed Benedict on whether he agreed that Catholic politicians who recently legalized abortion in Mexico City should rightfully be considered excommunicated, the response was "Yes."
Church law says anyone who procures a completed abortion is automatically excommunicated. But considering political support for abortion as equivalent to procurement would set new Vatican policy.
Benedict's spokesman, the Rev. Federico Lombardi, later said the pope was not setting a new policy and did not intend to formally excommunicate anyone, a rare process under church law separate from the doctrine of self-excommunication.
But Lombardi added that politicians who vote in favor of abortion should not receive the sacrament of Holy Communion. "Legislative action in favor of abortion is incompatible with participation in the Eucharist. ... Politicians exclude themselves from Communion," he said.
As many as 20,000 faithful waited in cold rain for a glimpse of Benedict in South America's largest city, then chanted "Bento, Bento" and waved flags of different South American nations as he greeted them in Portuguese and Spanish blessed them in Latin.
As well as abortion, Benedict is expected to address other challenges to Roman Catholicism during his trip, including the church's declining influence in Brazil, the rise of evangelism and a deep divide between rich and poor.
The Vatican also has promised that Benedict will deliver a tough message on poverty and crime during his five-day visit to the world's most populous Roman Catholic country.
Benedict's predecessor, John Paul II, visited Mexico and addressed Latin American bishops just three months after assuming the papacy. Benedict has waited two years for his first trip to the region, but he denied being "Eurocentric" or less concerned about poverty in the developing world than his predecessors.
"I love Latin America. I have traveled there a lot," he told reporters, adding that he is happy the time had come for the trip after focusing on more urgent problems in the Middle East and Africa.
Benedict, who visited Brazil as then-Cardinal Joseph Ratzinger in 1990, will celebrate several open-air Masses, including a canonization ceremony for Brazil's first native-born saint, and visit a church-run drug and alcohol rehabilitation center.
The tour ends on Sunday, when he will open the conference of Latin American and Caribbean bishops in the shrine city of Aparecida.