The National Organisation for Marriage’s co-founder Maggie Gallagher has said that same-sex marriage opponents must shift to trying to sustain a sub-culture of ‘traditional marriage’.

Gallagher also repeated her proclamation from last month that equal marriage was likely to happen in all 50 states within 18 months “whether we like it or not”.

Appearing on Relevant Radio, she said: “I believe that with the Windsor decision, we now clearly have five votes in the supreme court for gay marriage in all 50 states, so I think that’s going to happen very shortly.

“The appeals courts are beginning to order gay marriage even in states which do not have it yet.

“I think it’s very likely that we have to just live in the reality of if you look at what [Supreme court justice] Anthony Kennedy says in striking down DOMA laws, he has no respect at all for the classic understanding of marriage that would limit him.

“I’ve been saying since that decision, about 18 months until we have gay marriage in all 50 states in my judgement.

“Our big challenge is going to be how do we sustain a culture or sub-culture of marriage when our government defines and teaches that marriage is something rather different than what we believe.”

Unlike Gallagher, the National Organisation for Marriage is still attempting to fight equal marriage on a state-by-state basis, even attempting to defend Oregon’s same-sex marriage ban after the state declined to.

Blogging for GLAAD, Jeremy Hooper said her decision to repeatedly admit defeat was ‘peculiar’.

He said: “I still don’t get why she has so fully and utterly given up every fibre of fight.

“At this point, there isn’t even a case headed to the Supreme Court, and there will surely be at least a few more state-level fights, be at the ballot box or in front of a judge, before a case makes its way to the high court.

“The organization that Maggie co-founded, NOM, is certainly still trying its best to stave off inevitability.

“Why is Maggie going around town making the inevitability argument for us?”