In case the unwary reader assumes that I've done a volte face on this one, don't worry: I'm still the homophobic- bigoted-sky-fairy-worshipping-swivel-eyed-loon who opposes all right thinking people and rejects same sex 'marriage' as an act of legislative foolishness.
But putting that aside, there is a real question about why now the introduction of same sex 'marriage' seems for so many people to be an act of effortless commonsense while only a few years ago, it would have seemed (as it still seems to some of us) utterly ridiculous. Putting aside the bluster of liberal blowhards such as Patrick Harvie who go around like a crowd of latter day Nelsons pretending not to see any arguments against it whatsoever, there remains the question as to why arguments for same sex 'marriage' seem to have comparatively greater purchase on at least the chatterati than do arguments in favour of the status quo. Why is now the right time for same sex 'marriage' to be successfully introduced?
I suspect that at least part of the answer lies in a perfect storm of three ideas having achieved broad acceptance:
1) Marriage doesn't really matter and may even be harmful.
Down with that sort of thing...
Most of the combox arguments I've got into on this subject have usually involved the other side saying something like, 'Marriage isn't really that important for me but...'. Instead of being seen as the central social institution for bringing up children, it becomes little more than one way of doing this among many others and even (for some) an institution shot through with patriarchal values.
In short, if marriage doesn't matter, it doesn't matter what you do with it.
2) Men and women are identical
With this ring...
This is an odd one, because I don't think that anyone who's actually met a member of the opposite sex for more than thirty seconds really believes this deep down. But we all pretend we do. Given this pretense that men and women can do everything as well as each other and don't have deep seated psychological and physical differences, it neither matters that the upbringing of children benefits from the input of two different, but complementary approaches, nor that homosexuals find it impossible to form intimate relationships with the opposite sex.
In short, it doesn't matter whether you love a woman or a man, and it doesn't matter whether you are brought up by a woman or a man because men and women are the same (apart from trivial plumbing details).
3) Homosexuality is just as good as heterosexuality
'The New Normal' (no that's not a snide remark: it's the name of the TV show)
Putting aside any question of moral responsibility, there is no difference in moral value between loving someone of the opposite sex and loving someone of the same sex. In large measure, this follows on from 2): if men and women are the same, then what difference could there be between the two sorts of love? But even if 2) is rejected, then 3) seems to be widely held as an independent truism.
In short, if it's just as good to be gay as straight, why shouldn't gays get the opportunity to formalize their love as well?
I'm sure there are other 'memes' that could be mentioned here (not least the reduction of marriage to romantic love) but I'd hazard that the above are perhaps the most important in providing the background to the irresistibility of same sex 'marriage': start from the above, and same sex 'marriage' does indeed start to look reasonable. But from a Catholic (and indeed 'traditional') viewpoint, those three points do not look like truisms at all. On the contrary:
1*) Marriage is important because it provides the best environment within which to procreate and educate children.
2*) Women and men are very different from each other even though they are equal in value. It matters which one you love and it matters who brings up children.
3*) The inability to be intimate with a member of the opposite sex is an impairment of human flourishing whatever the cause of this inability (eg nature or nurture).
Clearly, there is an argument to be had on the truth of these three presuppositions, but I suspect it is at this deeper level of presupposition that any successful rational engagement has to proceed between the two sides rather than directly at the level of the rights and wrong of same sex 'marriage': accept 1), 2) and 3) and you're probably right to accept same sex marriage; accept 1*), 2*) and 3*) and you're right to reject it.
But anyway, who am I kidding? 'Rational engagement'? Some chance. This is going to be forced through by the UK and Scottish governments regardless.