So why would gay marriages be cardinal sin?
The leader of the Catholic Church in Scotland, Cardinal Keith O'Brien says government plans to introduce gay marriage are a "grotesque subversion of a universally accepted human right."
He likens support for it to support for slavery. ("Imagine for a moment that the government had decided to legalise slavery but assured us that 'no one will be forced to keep a slave.' Would such worthless assurances calm our fury? Would they justify dismantling a fundamental human right?")
The plans, he adds, are "madness" and he insists they will "shame the UK in the eyes of the world."
Strong stuff, Your Reverence!
Especially given that we already have gay civil partnerships in the UK which are gay marriages in all but name.
Civil partnerships convey upon participants exactly the same rights as civil marriage. And since their introduction in the UK in 2005 (we had the very first ceremony in Belfast) over 40,000 couples have walked down the civil aisle.
Changes to the law could mean that places of worship would be allowed (not forced) to host services, that there could be religious input into civil partnership ceremonies (there isn't at present) or even that we go the whole hog and recognise the unions as marriage.
It's this latter option that seems to be prompting most fury. But why?
Opponents appear to feel that allowing marriage between two people of the same sex who love each other and are committed to each other somehow demeans marriage as we know it - marriage, that is, between two people of different sex who also love each other and are committed to each other.
But far from destabilising the institution couldn't it equally be argued that the demand for gay marriage actually endorses and bolsters it?
Religious leaders, you would think, would welcome the idea of people prepared to commit to each other. Especially those who would wish to do this with the blessing of their church. Instead some clergy (not all, I know) seem more comfortable with this weird halfway house which recognises legal contract but not human love.
Faith, hope and lack of clarity ...
As a married woman (civil ceremony) I just cannot see in any way how gay people also being allowed to describe and regard themselves as "married" would be anything but positive.
I certainly don't see it grotesque or shameful (are civil partnerships, which are seen as "almost marriage", to be regarded as slightly grotesque and slightly shameful?)
The whole thing just smacks of a cruel nitpicking.
We have moved on from the love that dare not speak its name to the love that dare not speak its name in the same terms as the rest of us.
Cardinal O'Brien argues: "The natural law teaching of what marriage is is quite simple.
It is natural for a man and woman to be together for the procreation and education of children and for their own mutual love."
Oddly enough this definition would seem to leave out on a limb older people who get married in their twilight years and would not, of course , be getting "together for the procreation of children."
But it's not the logic that's the biggest problem here. It's the cruel rhetoric.
Above all the lack of compassion.
And wasn't that something churches were supposed to major in?