An openly gay person has been invited to speak about homosexuality during the significant Vatican-approved convention on the family in Philadelphia, according to RNS.

Both conservative and liberal Catholics have criticised the Pope's decision to allow Ron Belgau to speak at The World Meeting of Families convention.

Belgau is homosexual but is committed to being celibate as he follows the Christian ethic that says homosexual activity is sinful.

American Catholic opinion has been growing more accommodating of LGBT rights, and Pope Francis has made it clear he wants the Church to be more welcoming to gay people, while not wanting to change doctrine.

Liberal Catholics have protested his being the only LGBT voice, as they believe the Church should find ways to accept sexually active LGBT members.

Belgau curates a blog, Spiritual Friendship, with New Testament professor Wesley Hill, that encourages gay Christians in living chaste lives through strong friendships that focus on spiritual growth.

Belgau acknowledges the challenge of choosing chastity and says "I'm not banging people over the head with that."

Many Catholic leaders find this position too liberal and are uneasy with both the Pope and Belgau's positions.

Some leaders have voiced disapproval that Belgau is vocal about his sexual orientation and is not trying to change it.

There are "certain people who say we shouldn't talk about this but who almost can't stop" talking about it, Belgau said. They insist on sharing their views on the topic, "but then if I try to talk about my own experience they say, 'We shouldn't be talking about this.'"

He believes that the topic is unavoidable to the extent that if World Meeting of Families did not address it, "that itself would have been a major source of news coverage."

Belgau is giving a talk entitled "Always Consider the Person" and hopes to echo and elaborate upon the Pope's message of inclusivity.

"My biggest theme would simply be moving away from the culture wars' focus on 'us versus them,' and saying, respond to people as people," Belgau said.

"There's way more focus on gays and lesbians who fall short of the ideal than there is on straight Catholics who fall short of the ideal," he said.

Commenting on the recent dismissal of a teacher from a Catholic school in suburban Philadelphia over her marriage to her partner, Belgau said "it seems to shake out that single women who get pregnant and gays and lesbians tend to bear the brunt of this maintaining Catholic identity."

He is aware that his views will attract criticism from some of the more orthodox Catholic audience, but added "I think in some ways those who have been hurt by church, those alienated by the church or in some way outside the church, are a more important audience."

The convention, The World Meeting of Families, is one of the key reasons Pope Francis has travelled to the USA and is happening on 24 September.