The rector of Melbourne's most prestigious Catholic college says the Church needs to reflect on the divide between its stance on same-sex marriage and that of young people.
In a newsletter, Xavier College rector Chris Middleton said Catholic leaders "face a difficult path to tread in discerning how the Church should have its voice heard in this debate".
Fr Middleton said it was important to distinguish between the argument about public policy in a secular state and moral positions.
"After all, the vote relates to marriage as a civil right, and is not in essence about the Catholic sacramental understanding of marriage," he wrote.
Considerations of religious liberty are "more likely to be respected if the Church is not seen as an uncompromising enemy of same-sex marriage in civil society" and Catholic leaders should be careful to avoid charges of hypocrisy.
"To be brutally honest, the Church speaking out in controversial areas around sexuality risks being mired in vitriolic attacks on its credibility in the aftermath of the Royal Commission, (into institutional child sexual " Fr Middleton wrote.
He said there was a clear disconnect between the Church's public opposition to same-sex civil marriage and young people, including those in religious schools.
"In my experience, there is almost total unanimity amongst the young in favour of same-sex marriage, and arguments against it have almost no impact on them. This has been the experience in many similar countries," he wrote.
"They are idealistic in the value they ascribe to love, the primary gospel value. Any argument against same-sex-marriage must respectfully address these core values, or they will fail a basic test of credibility with our young."