Former president Mary McAleese has described as "unacceptable" and "ugly" the language used in a Vatican document that says the Catholic Church cannot bless single-sex unions.
The Vatican said on Monday that the church does not have the power to bless same-sex unions despite their "positive elements", saying it was impossible for God to "bless sin".
The Congregation for the Doctrine of the Faith, which is responsible for defending church doctrine, said that blessings are not allowed because what is to be blessed needs to be "objectively and positively ordered to receive and express grace, according to the designs of God inscribed in creation, and fully revealed by Christ the Lord".
Speaking on RTÉ's News at One, Dr McAleese, who is a canon lawyer, said it is "astounding" that the church has said to gay people that it cannot "receive or express grace".
"They added an explanatory memorandum in language, which is simply unacceptable. It's ugly. It has jarred with a lot of priests, bishops and some Cardinals.
"To tell gay people who have been so damaged by church doctrine, which has used dreadful language that is conducive to homophobia, to say, of gay couples, as this document goes, they cannot receive or express grace, that's the astounding thing.
"To say that, but at the same time they can bless a pot plant or a pet, is not acceptable."
Dr McAleese said she believes Pope Francis is hearing voices on all sides, but she said his job is to give leadership, "it is just to ride two horses at the same time".
She said there is "huge" evidence of the church's role in how children have been exposed to teachings that that conduce to homophobia, by presenting, same-sex married couples as sinful.
Listen to Mary McAleese's interview on RTÉ's News at One
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"All you have to do is look at the research into school bullying in relation to homophobia.
"You only have to look at that for some of the young men, particularly young gay men, are overrepresented by three times in the stats on anxiety, and nervous difficulties, psychiatric problems, and are deeply linked to suicidal ideation.
"I can leave responsibility for that at the door of those who do and say things that conduce to embedded homophobia and attitudes that conduce to the hatred of homosexuals.
"I can lay it at the door of any institution, which claims to be created by God in order to spread love. And it does not do that, in relation to gay men, women and children."
Dr McAleese said there are "questions to ask" about the teachings that children are exposed to, and the language used by the church.
"So I think that we have big questions to ask about the kind of catechesis that our children are exposed to.
"And I think that we are entitled to ask those questions in a jurisdiction where such significant input into our education comes from faith-based institutions which are able to use language like 'disordered, intrinsically evil, unable to receive or express grace'. This is awful language."
Priest says he would bless marriage of same-sex couple
The Association of Catholic Priests in Ireland has said the statement from the Vatican that priests cannot bless same-sex marriages or unions is "disappointing and appalling" and does not reflect the lived experience of the church.
Fr Tim Hazelwood of the ACPI, who is a priest in Killeagh in Youghal, Co Cork, said that Pope Francis is in a very difficult position on the issue of gay unions and is trying to balance two opposing views within the church.
Speaking on RTÉ's Morning Ireland, he said the Pope had said "very positive things about inclusiveness" and including gay people and others on the margins.
Fr Hazelwood said that this week he blessed shamrock that grows in the ground and would likewise happily bless two people standing in front of him who are committing to love each other.
He said that most priests who interact with people in their parishes meet families with someone in their family in a same-sex relationship.
Fr Hazelwood said: "Our experience is that they are lovely couples and to hear [the Vatican statement] that their relationship is sinful, I wonder how many of them know and meet and interact with those people."
Separately, Bishop of Derry Donal McKeown said he agrees with Pope Francis that the union between same-sex couples should not be blessed as if it was the union between a man and a woman.
Speaking on RTÉ's Today with Claire Byrne, Bishop McKeown said: "I have plenty of friends who are homosexual, including people who are in same-sex relationships, and I can walk with them and be friendly with them and be as courteous and as gracious, but you can only walk so far.
"I am not prepared to say that this is the same as the sacrament of Christ's union with his church."
Bishop McKeown said he has "every respect for people" who disagree with him, but added: "Christ was very clear that there are awkward truths in Christianity.
He explained that St Paul said "marriage between a husband and wife is the sign of Christ's love for his church".
"Marriage is a sacrament that is a sign of Christ's love for his church, in other words, other types of relationships exist, which are not marriage."
He said priests are "not entitled" to regard same-sex couples as married "in the sense of being a sacrament of Christ's price relationship with the church".
