Benedict spoke to reporters aboard a special Alitalia flight that carried him to central Mexico, where a swelling crowd gathered to cheer him along his path from airport on his first visit to Spanish-speaking Latin America.
The pope said a lust for money was behind the drug violence that has claimed more than 47,000 lives in the country since a government crackdown began in 2006.
On Monday, Benedict will head for Cuba. He said it is "evident that Marxist ideology as it was conceived no longer responds to reality," and he urged Cubans to "find new models, with patience, and in a constructive way."
The comment about Marxism, in response to questions from a journalist, was as blunt as anything his predecessor, John Paul II, made during his groundbreaking 1998 trip to Cuba, though the earlier pope is widely credited with helping bring down socialism in eastern Europe.
Benedict cautioned that "this process requires patience and also decisiveness."
Asked about reports that dissidents in Cuba are still routinely harassed and arrested, including in the weeks leading up to his visit, Benedict said that the church wants "to help in the spirit of dialogue to avoid trauma and to help bring about a just and fraternal society, as we want in the whole world."
"We want to collaborate in this sense, and it's obvious that the church is always on the side of freedom, freedom of conscience, freedom of religion," the pope said.
Benedict said John Paul's visit to Cuba ushered in a slow process of dialogue and cooperation between church and state on the island.
During that trip, John Paul made a clear if cautious call for then-President Fidel Castro to open up Cuban society, take steady if gradual steps toward democracy and give the church a greater voice. He also called for the release of political prisoners while giving Castro what he wanted, a condemnation of the U.S. embargo.
Asked about Benedict's statement, Cuban Foreign Minister Bruno Rodriguez said the government respects all opinions. "We consider the exchange of ideas to be useful. Our people have deep convictions developed over the course of our history," he said, adding that the Cuban system "is a democratic social project ... which is constantly perfecting itself."
In Mexico, Benedict said, violence is destroying the nation's young.
The "great responsibility of the church is to educate the conscience, teach moral responsibility and strip off the mask (from) the idolatry of money that enslaves mankind, and unmask the false promise, this lie that is behind" the drug culture, he said.
It is a message that Enrique Abundes, one of thousands lining the papal route, was waiting to hear. The 46-year-old shoe-factory worker and father of five said he believed Benedict would inspire Mexicans to keep their children away from the temptations of organized crime.
"The pope's visit to our city will call attention to the violence and, for us, to be good examples to our children," he said.
The weeklong trip to Mexico and Cuba, Benedict's first to both countries, will be a test of stamina for the pope, who turns 85 next month. At the airport on Friday in Rome, the pope used a cane, apparently for the first time in public, as he walked about 100 yards (meters) to the airliner's steps.
Papal aides, speaking on condition of anonymity, said Benedict has been using the cane in private for about two months because it makes him feel more secure, not for any medical reason. Last fall, Benedict started using a wheeled platform to navigate the vast spaces of St. Peter's Basilica during ceremonies. The Vatican has said that device was employed to help the pope save his energy.
John Paul II was just 58 when he made the first of five visits to Mexico, where he is literally venerated by many Mexican Catholics.
The pope's plane set down Friday afternoon in Guanajuato, a deeply conservative state in sun-baked central Mexico, and his route into the city of Leon was thronged with thousands of people eager to get a glimpse of the pontiff.
Maria Jesus Caudillo, a stationery story owner in Leon, found a spot early on the Popemobile route with her four nieces and nephews.
"John Paul came to Mexico but never to Leon and never this pope," she said. "It's a miracle that in all the country, he chose to come to Leon."
Volunteers led the crowds in chants of "Benedicto! Benedicto!" as passing drivers pounded their horns in encouragement. Vendors sold Benedict buttons, T-shirts, Vatican flags and key chains with the image of the pope and the Virgin of Guadalupe.
By midafternoon, many spectators sought refuge from the hot sun under trees on the roadside, fanning themselves or even falling asleep.
Vendors complained about small crowds and lack of sales.
"We thought there would be more people," said Agustin Rodriguez, a 55-year old fruit seller.
Jorge Alfredo, a 15-year-old delivery boy, rolled his bicycle down the sidewalk past drowsy spectators and said he wouldn't be waiting around to see Benedict. None of his friends would be coming either, he said.
"They prefer the other pope," he said.
Many businesses and schools had closed for the day in Leon, and thousands of people were traveling in on buses from across the country.
Still about 30 percent of the city's 6,000 hotel rooms were still empty, said Fabiola Vera, president of the Association of Hotels and Motels of Leon. She said people may have been discouraged by rumors that there weren't enough rooms.
The main campground in Leon, meant for tens of thousands of pilgrims, remained empty. The only evidence of preparations early Friday were about a dozen portable toilets, a single police patrol and a group of three men and a woman putting up a tent to sell T-shirts and photos of Benedict.
Church officials say as many as 300,000 people are expected for Sunday's Mass and Carlos Aguiar, president of the Mexican Episcopal Conference, said he expected the faithful to begin arriving later Friday.
Benedict is visiting a church battling to overcome painful setbacks that include legalized abortion and gay marriage in the capital of the most populous Catholic country in the Spanish-speaking world.
Guanajuato's constitution declares that life begins at conception and bars abortion with extremely limited exceptions. Seven women were jailed there in 2010 for the deaths of their newborns and later released. The women said they had miscarriages, not abortions.
Benedict's church is encouraging more such laws across Mexico, and a measure before Congress would strip away many of the remaining restrictions on religion that were imposed during conflicts more than a century ago.
Church leaders also are trying to overcome a scandal over the most influential Mexican figure in the church.
The Rev. Marcial Maciel founded the Legionaries of Christ order, which John Paul II praised as a model of rectitude. But a series of investigations forced the order to acknowledge in 2010 that Maciel had sexually abused seminarians and fathered three children. Church documents released in a book this week reveal the Vatican had been told of Maciel's drug abuse and pederasty decades ago.
Contributing to this report were Associated Press writers Michael Weissenstein, E. Eduardo Castillo and Dario Lopez-Mills in Leon, Mexico, and Frances D'Emilio in Rome.