Journalist Bruce Arnold says Ireland is heading into a "bleak and terrible" future if the institution of marriage and procreation is undermined.

The journalist has published a new study paper, "Same-Sex Marriage in the Irish Constitution", in opposition to the same-sex marriage referendum, along with other members of a Christian group called the Pauline Circle.

Mr Arnold says that while a heterosexual and homosexual couple are different, "they're not unequal".

"The use of the term 'equality' as a description for this legislation is, in my view, perverse and illogical," he said.

"We're all equal; and the equality between heterosexual couples and same-sex couples is an equality that's framed by two approaches to the legislative framework: one of them being marriage, the other being civil partnership".

He says the if marriage is granted to same-sex partners, they will then be unequal - as homosexual couples "will have two methods of joining themselves together and married people will have marriage".

He says there is a pressure group made up of people who want to rush the legislation on marriage equality through.

And he claims the Justice Minister Frances Fitzgerald has fallen for it "hook, line and sinker".

Mr Arnold told the Pat Kenny Show here on Newstalk that marriage and procreation has to be protected.