Calling things equal which are in fact not equal is an error.
Every society I have ever heard of has a ritual of marriage - it everywhere serves the purpose of celebrating the preferred precondition for bringing new people into the tribe/community/nation etc.
It also has a number of spinoffs, such as who is snogging with whom, who is the biggest and nastiest with the mostest, who inherits from whom etc.
Now, a marriage which can, probably or possibly produce children is a rather different thing from a marriage which cannot.
Many marriages, especially between older couples, won't produce children. There is however no meaningful dividing line between actually fertile/infertile, possibly fertile/infertile, intentionally fertile/infertile couples.
A same-sex couple however, is not of itself, and can never be, fertile. (We'll just skip cloning and test-tube gene merging here, shall we?)
Bluntly, I consider it bizarre that persons who have an aversion to sex (with the opposite sex) nevertheless wish to have children ...
... unless of course we disregard the notion of having sex (with the opposite sex) as a precondition for having children.
Asexual or industrial conception is an indignity which we have foisted onto domesticated animals, but I don't look forward to it becoming normal, accepted or for that matter, even tolerated in a civilised society.
There are profound consequences of removing hetrosexuality from the notion of society's definition of marriage, concerning which I have yet to see any meaningful public discussion. Such discussion as one does see is usually name-calling.
Such discussion may possibly occur, if as a society, we remove this issue from party politics, and put it to the people as a plebicite. (I'm not really comfortable with the words "conscience" and "parliament" in the same sentence).
The advocates of same-sex marriage will presumably be content with such a notion, as it is routinely claimed that the proposal has overwhelming public support.
But I'm not holding my breath on that last point. Such private conversations I've had with same-sex marriage advocates bring forth obfuscation and excuses as to why not.
