Could the same logic not be applied to say blacks and whites marrying? Oh wait, it was up until 1967 when they finally legalised mixed marriages in America. It's sad to see almost fifty years after these arguments were made in America, that an Irish group would be using them to once again discriminate against a group of people here in Ireland.
Check out their website -
The Iona Institute | Welcome to the Iona Institute Website
It's chock full of anti-gay, anti-Muslim articles.