Pope Francis previews U.S. itinerary on flight from Asia trip

ROME -- The official reason for Pope Francis' first trip to the U.S. this September is to take part in what is already being billed as a "massive Catholic rally for families" in Philadelphia, but no one should expect it to be that simple.

CBS News' Allen Pizzey says, first of all, Francis' record for rallies so far makes it a massive challenge for the organizers. His final mass in Manila on Sunday drew an estimated and unprecedented 6 million people.

Archbishop Joseph Kurtz on Pope Francis’ contemporary leadership

Speaking to reporters on his flight home from Asia, Francis laid out some of his U.S. itinerary. And in a preview of the message he'll bring to the U.S., the pontiff said he would have liked to enter the U.S. by way of the Mexican border.

He said it would have been "a beautiful thing... as a sign of brotherhood and of help to the immigrants."

Previous Papal visits to the U.S. have been more symbolic than controversial.

Pope Paul VI met then President John F. Kennedy, John Paul II held a huge Mass in Yankee Stadium and Benedict XVI prayed at Ground Zero.

Francis will canonize 18th-century missionary Junipero Serra whose role in converting Native Americans is considered controversial. He's also expected to address Congress and the United Nations with a message that will probably please and trouble in equal measure.

"I think for the Vatican, the most important goal is to draw attention to social justice and immigration and the climate, but at the same time, they have to get everyone on board with this message by saying that Pope Francis is a traditionalist on issues like the family," University of Notre Dame Professor of New Testament and Early Christianity Candida Moss said.

But he has a very nontraditional way of making a point.

On his plane back from the Philippines, Francis said Catholics "don't have to breed like rabbits," and should instead practice "responsible parenting." At the same time, he warned against what he termed "insidious attacks" against the family, a remark widely interpreted as a reference to gay marriage.

There are plans for Pope Francis to visit Ecuador, Bolivia and Paraguay this year, too, as well as the Central African Republic and Uganda, but all of them together probably won't match whatever happens when he hits U.S. shores.