In March, Mattson was invited to Notre Dame to affirm same-sex attracted people find healing and fulfillment by faithfully living out the teachings of the Church.
Sponsored by campus group Students for Child-Oriented Policy (SCOP), Mattson's talk, "Same-Sex Attraction and Catholicism," traced his embrace of the Faith and subsequent journey out of the gay lifestyle.
"I am actually somebody, believe it or not, who came into the Catholic Church because of the Church's teaching on sexuality and homosexuality," he told students.
In his testimony, he emphasized how Catholic teaching awakened him to the transformative nature of God's love.
"The gift that [the Church] gives to me is to constantly remind me of how beloved I am by God," he explained. "And part of that ... is to guide me in the path that will lead to human fulfillment."
But some students lashed out against his reinforcement of Church doctrine.
In an April 6 op-ed for university newspaper The Observer, sophomores Michael O'Dea and Mary Szromba accused Mattson of painting a "repressive picture of sexuality."
"Does Notre Dame Fear the Queers?" trashed Mattson's testimony as having "no basis in biological, psychological or sociological sciences."
After accusing Mattson of scientific ignorance, O'Dea and Szromba slammed his orthodoxy as merely "his interpretation" of Catholic doctrine.
To justify their position, they pointed to a body of heterodox German, Austrian and Swiss theologians whose "interpretations" depart from Church teaching on active homosexuality:
Despite Mattson's confidence in his interpretation of Catholic doctrine, it would appear that actual theologians are not totally in agreement. This is demonstrated in Church 2011, a memorandum signed by 260 Catholic theologians, which advocates for greater acceptance of same-sex relationships. It argues that the Church's teachings do "not require the exclusion of people who responsibly live out love, faithfulness and mutual care in same-sex partnerships."
"It is clear that there is much to discuss on this topic," they added, "and we believe that there is no better place to have this theological and political debate than America's preeminent Catholic university."
But, the pair complained, Notre Dame is unsympathetic to students who dissent from Church teaching on homosexuality.
This group "is not allowed to speak out against current Catholic doctrine on LGBTQ," they wrote. "Notre Dame has persistently smothered such efforts of student expression."
But others students voiced strong support for Mattson and his message.
Shaun Evans, SCOP president, praised Mattson for his unrelenting fight for holiness. "We believe his personal testimony ... is a powerful witness to the peace that can be found when one seeks to live out authentic love united to the truth about human sexual complementarity," he said.
Junior Teresa Kaza echoed Evans' praise in an article for The Irish Rover, a student publication devoted to preserving the Catholic identity of Notre Dame
"Rather than defining oneself by one's sexual orientation," Kaza observed, "Mattson discussed viewing people in terms of being 'male and female who have experiences and attractions,' who are fundamentally children of God. This is in line with the Church's documents on homosexuality."
Kaza also affirmed that Mattson's message reinforces Church doctrine. Quoting from the Letter to the Bishops of the Catholic Church on the Pastoral Care of Homosexual Persons, she wrote:
The human person, made in the image and likeness of God, can hardly be adequately described by a reductionist reference to his or her sexual orientation. ... Today, the Church provides a badly needed context for the care of the human person when she refuses to consider the person as a "heterosexual" or a "homosexual" and insists that every person has a fundamental identity: the creature of God, and by grace, his child and heir to eternal life.
Mattson's journey out of the gay lifestyle into authentic Catholicism affirms this teaching.
Reflecting on his path, he told his audience at Notre Dame, "I have never felt more welcomed and loved than in the Catholic Church."