Marriage and biology

Someone's seen my post, or Twitter feed:

Functionally, a dud!

I note Mr (MP)'s talking about 'genuine commitment to marriage equality'.

Of course, given the biological basis for marriage, I'm all for equality as well. What does puzzle me is how the current debate pretends that there is no functional issue here, but one of mere 'being in love'. 

Marriage has in view procreation. Eons of evolution have shaped this, no law, no culture, such that reproduction requires a zygote and no pair of the same sex can make one.

Thus the current debate is about marriage debasement, commoditisation of children and the intrusion of the law into the fairytale world of happily ever after romance.

I know that the law will probably be changed: the real world has never stopped legislators, but let's not pretend that there is a biological equality of function between a same sex pair (who cannot sexually reproduce) and a mixed sex pair who are able to make babies all on their own and that said babies will grow up in the company of their parents.