My comment (added in the comments box)...
"Gay marriage" is a legal fiction. A man can no more actually marry a man, than he can marry his left foot, regardless of what the paperwork says. I note that Graeme Archer, who considers himself conservative, provides no argument at all based on the nature of human sexuality (male/female) and addresses zero questions about the complementarity of the sexes. He simply assumes what needs to be proved - that a man/man relationship is the same thing. But this argument essentially means that male-ness and female-ness either don't exist, or are entirely interchangeable (which amounts to the same as not existing).
Archer's assumption throughout his piece is simply that marriage is whatever a majority say it is. This argument is insane, and takes the idea of democracy to a ludicrous extreme. It provides no logical reason why marriage can't involve one man and four women, or a brother and sister, or a man and his grand-daughter, or a man and his horse. If marriage is just whatever a majority of the voters, or a majority of the MPs, say it is, then ultimately marriage is nothing. It's completely arbitrary - one definition today; but perhaps the voters tomorrow will decide that "marriage" is the moon, or my left foot. This approach ultimately reduces marriage to nothing except "some sort of relationship with some sort of tax benefits".
Hence, it is correct to say that the redefinition of marriage is not simply a question of "extending the benefits of marriage". It "extends" by eliminating. The concept of "marriage" pushed by proponents of "gay marriage" has little to do with historic conceptions of marriage. That's why widespread easy divorce and acceptance of adultery and promiscuity as socially normal were necessary stepping stones before we could reach this stage.
Marriage is not a trophy, or a prize for society to award to favoured groups. Marriage is the exclusive commitment of two sexually complementary beings - a man and a woman - to live together as husband and wife, in a relationship which can, if so blessed, be fruitful in producing and raising up children. Hence I urge the voters of Ireland to reject the legal fiction, the oxymoronic nothing, of "gay marriage".