A recent discussion on the impending referendum in the Republic of Ireland on adding the amendment "Marriage may be contracted in accordance with law by two persons without distinction as to their sex" to the constitution led me to this video by something called the Iona Institute, a pressure group who advocate voting against the amendment. I'm quite removed from American politics so it could be that the debate has played out exactly the same way as it did in the USA, but I've not personally seen the argument framed in exactly that way before.
The Iona Institute's argument is summarised in the video as "If you think that a mother's love is unique and irreplaceable, and so is a father's love, then vote 'No' on May 22nd". My question is: can this viewpoint actually be justified? As someone who is raised by a single parent, my own perspective is obviously likely to be biased, but I'm wondering whether this debate can be settled with evidence rather than opinions.