Faith-based objections have no place in the secular same-sex marriage debate in Northern Ireland, the son of former Irish president Mary McAleese said.
It is the only part of the UK in which what campaigners term marriage equality has not been legalised due to religious-inspired opposition from its largest party, DUP.
Justin McAleese (pictured, centre) was a prominent campaigner in the Irish Republic's watershed referendum campaign in 2015, when he discussed his experience growing up as a gay man.
Mr McAleese said he had a "huge problem" with the level of leadership in the Catholic Church but urged advocates of change to engage in difficult conversations with those who think differently.
He said: "Faith has no place in secular, registry office marriage."
The campaigner attended an event in Belfast as part of the annual Pride festival.
The Democratic Unionists, Prime Minister Theresa May's close allies, hold that Christian marriage is between a man and a woman and have used a parliamentary mechanism at Stormont to veto efforts to legislate in Northern Ireland.
Mr McAleese said the Church of Ireland and Catholic Church was entitled to its definition of marriage but should not be able to force that view on everyone else in the secular world.
He said: "Coming at this debate through the prism of one definition of marriage from the tradition of religion is simply not good enough when you are talking about civil registry office marriage in secular Northern Ireland."
He added: "We need to talk about marriage... one kind of marriage, everyone equal, that would be progress."
When the now-suspended Stormont Assembly was operating its members voted in favour of change, while public opinion polls show a majority of above 70% back social liberalisation.
Former president Mary McAleese was an outspoken advocate for same-sex marriage during Ireland's referendum campaign which saw such unions legalised.
Her son Justin has said he wanted to win a seat in the next Irish general election.
He called for a proper debate around sexual health and education in the Republic, claiming the authorities were "away behind" on addressing some of these issues.
"You should leave school knowing how you can ensure your own sexual health.
"There is a lot of work to be done but nothing has happened since the referendum."
Earlier, Barnardo's became the first children's charity in Northern Ireland to publicly voice support for the recognition of same-sex marriage.
With devolved government at Stormont remaining in suspension since January 2017, earlier this year Labour MP Conor McGinn tried unsuccessfully to force the policy through Westminster via a private members bill.
Koulla Yiasouma, Northern Ireland Commissioner for Children and Young People, said: "It is clear the current situation in terms of same sex marriage in Northern Ireland is untenable and legislation needs to be enacted as soon as possible to address this discrimination and its direct and indirect effect on children and young people."
CAMPAIGNER: SAME-SEX MARRIAGE OPPONENTS RISK ALIENATING A GENERATION IN NI
Opponents of same-sex marriage reform risk alienating a generation in Northern Ireland, a leading campaigner will say later.
Ged Killen, a gay Catholic and Labour MP from Glasgow, is married to a man from Northern Ireland.
He will address the annual Amnesty International Pride lecture in Belfast later and will say it is anti-democratic for Westminster to refuse to legislate on the matter in the absence of devolved government at Stormont.
"Make no mistake. Same-sex marriage in Northern Ireland will happen.
"Those who stand opposed risk alienating a generation.
"The children of future married same-sex couples, their friends and their families will not forgive nor forget those who stood in the way of equality."
Northern Ireland is the only part of the UK in which same-sex marriage has not been legalised due to opposition from its largest party, the DUP.
The Republic of Ireland voted to allow the ceremony in 2015.
Theresa May's Democratic Unionist allies hold that Christian marriage is between a man and a woman and have used a parliamentary mechanism at Stormont to veto efforts to legislate.
When the now-suspended Assembly was operating its members voted in favour of change while public opinion polls show a majority of above 70% back social liberalisation.
Mr Killen will say there is also a clear majority at Westminster who would vote to extend the right of marriage in Northern Ireland in the absence of a devolved Assembly in Belfast.
"The opponents of same-sex marriage seek to impose a minority view on the LGBT community in Northern Ireland through a technicality.
"Under these circumstances, it is anti-democratic not to legislate for same-sex marriage and Westminster has a moral and a democratic obligation to do so.
"Instead of facing a vote, they now run away, using cheap parlour tricks and the machinations of parliamentary processes and the petition of concern to deny the will of the people of Northern Ireland.
"It can only be described as one thing, a stitch-up to prevent people from claiming their rights."
He urged the Prime Minister to decide whether her deal with the DUP to prop up the minority Government, which preserved her "fragile" grip on power, was worth perpetuating ongoing discrimination against the LGBT+ community in Northern Ireland.
Mr Killen has previously acknowledged that his relationship with religion had not always been an easy one.
In 2012 he wrote to the then head of the Catholic Church in Scotland, Cardinal Keith O'Brien, challenging him on anti-LGBT comments he had allegedly been making in the media.
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Liam McBurney / PA Wire.