Blame it on those San Francisco values.

That’s what the Rev. Joseph Illo believes is driving the uproar around his decision not to train girls to be altar servers at Star of the Sea Catholic Church.

“I think the Church’s insistence on the distinctiveness of gender, that being male and female is a charism given by God that enables a person to do certain things and not other things, that gender is not just accidental, cannot be changed at whim, is deeply part of the essence of a person — that’s why this is such a big thing in San Francisco,” Illo told Crux.

He said critics of the policy are really reacting against the Church’s all-male priesthood.

“The assistants of priests at the altar should be male, because the priesthood is a fatherhood, not a motherhood,” he said.

Plus, he said in a recent statement, boys “end up losing interest” if girls are allowed to serve.

Illo’s decision to ban girls pits tradition and concern about the declining number of clergy against those agitating for greater visibility for women in the Church. While some firmly believe that serving at the altar could lead to priestly vocations, others say involving girls in the celebration of the Eucharist is a way to make them feel welcomed and valued.

For centuries, only boys were permitted to serve at the altar. But a revision to canon law in 1983 allowed “lay persons” to be altar servers, leading some priests and bishops to conclude the ministry was open to girls.

Pope John Paul II agreed, and in 1994, the Congregation for Divine Worship issued a clarification stating that girls and women could join boys and men as altar servers.

But that same document made two other points: That it is “very appropriate to follow the noble tradition of having boys serve at the altar,” and that being an altar server could lead to priestly vocations — one of Illo’s arguments in favor of all-male servers.

Other clergy disagree.

Bishop Christopher Coyne, newly installed leader of Vermont’s Catholics, said in a 2013 appearance on Catholic TV that he doubted the presence of female altar services would negatively impact a young man’s vocation discernment. Plus, barring girls might discourage mothers from encouraging their sons to consider the priesthood, he said.

“It’s a way of welcoming them to the table, of saying they have an important role in the liturgy, that they’re not second-class citizens because they’re girls,” he said. “I want to encourage the girls to see the Church as inviting,” prompting them to pass on the faith and encourage vocations when they have children.

Brother Emanuel Franco, who runs the altar server program at Saint Raphael Church in Los Angeles, said liturgy is about more than a single priest, so it “doesn’t make sense” to him to exclude girls.

“It would make sense if liturgy was done only by priests, but liturgy is a team. You have priests, deacons, lectors, and ministers. You have a lot of people serving, so it’s good to have girls and boys at the altar,” he told Crux. Plus, he said, boys and girls are used to collaborating in school and in social settings, so he’s “never heard any complaints” from boys about female altar servers.

And the Rev. Paul Sustayta, pastor of Saint Andrew Catholic Church in Pasadena, California, said more important than gender is an attitude of prayerfulness and reverence, using servers “who want to be up there because they want to serve the Lord,” he said.

“It’s really all in the training, it’s so important,” he said. “If you have boys and girls who are trained well, who know the liturgy, who understand the importance of the Eucharist, I think they really do well.”

Girls have been permitted to serve as altar services in parishes in every American diocese since the 1990s but one: the Diocese of Lincoln, Nebraska.

“Very few Catholic families have ever requested that girls be permitted to serve at the altar in the Diocese of Lincoln,” JD Flynn, a diocesan spokesman, said. “This is, I think, in part because of the positive influence of women religious in Lincoln’s schools and parishes, and because of liturgical formation focused, from a young age, on the serious vocation of laity to full, active, and conscious participation in the Mass through contemplation, thanksgiving, and adoration.”

The decision of whether to use girls as altar servers lies not with the bishop, however, but with the individual pastor. And those working in parishes that have decided to use only boys say the results are worth it.

In Phoenix, the rector of Saints Simon and Jude Cathedral made headlines in 2011 when he announced that girls would no longer be invited to serve as altar servers. He said at the time that altar service should be reserved for boys to help them discern religious vocations.

Andrea Diaz, the cathedral’s director of faith formation, said that in the years after the decision, programs for boys and girls have flourished.

“The number of boys has increased in altar serving,” she said. “It’s great to see strong men living out their faith and building up that culture of life.”

There are new opportunities for girls at the cathedral, she said, such as serving as sacristans. “They are the ones responsible for preparing the vessels and linens for Mass,” she said. Plus, there is a prayer group for young girls, whose members receive a mantilla, or lace head covering, to wear to Mass.

Little data exists about Catholic attitudes toward female altar servers. And the notion that including girls in the ministry drives away boys and reduces vocations to the priesthood hasn’t been studied.

In reports compiled for the US Conference of Catholic Bishops about the demographics of new priests and men and women entering religious life, the Catholic research group CARA asked only if the individual was an altar server, not if serving at Mass played an important role in their vocation. (Of priests ordained last year, 80 percent had been altar servers. Of the women and men entering religious life, about a third were.)

Illo, the San Francisco priest, said he knows his views on gender, which he believes “gives a person the capacity to fill a specific role,” aren’t popular. “I know most people wouldn’t agree with that, but the fact is, that’s the teaching of the Catholic Church,” he said.

One unexpected benefit of Illo’s decision has been a financial one: As of Tuesday, more than $47,000 has been raised to donate to Star of the Sea by supporters of Church Militant TV, a conservative video ministry headed by Michael Voris.

Known for his attacks on Catholic moderates, including bishops, Voris has been barred from calling his ministry “Catholic” and banned from speaking in at least one Catholic diocese because of controversial comments about Church leaders and other religions.

But Illo isn’t complaining. He said he’ll use the money for a new children’s chorister program.

“I had to present a budget in the red to the finance council last week and they said, ‘Where are you going to come up with the money?’ And I said, ‘Oh I don’t know, God will provide.’ And suddenly this money drops out of the sky.”