Let's see if we can debate the place of marriage in our society without divorcing ourselves from reality and the importance of preserving age-old customs

I've just got back from a trip to London to celebrate a friend's wedding. It was fantastic. I love weddings. I think marriage is a wonderful thing and believe that such a commitment before friends and family (and God, if you so believe) can create a bond beyond a de facto promise. It's sacred and worth preserving.

Which is why I support Louisa Wall's gay marriage bill.

Since the bill -- which would define marriage legally for the first time, as a commitment between two consenting adults regardless of gender -- there's been a lot of talk about saving marriage from homosexuality.

New Zealand First MP Richard Prosser, for example, says:

"It's about preserving the institution of marriage . . . I've got nothing against gays."

But what's being missed in this debate so far is that purity and preservation are not the same thing; sometimes the best way to ensure something stays precious and relevant is to let it evolve.

The best way to preserve marriage is surely to make it inclusive and to embrace all those who want to honour the love and commitment that stand at the heart of the institution. Let's say that for marriage all you need is love, love, love between two consenting adults and in that way encourage more people to marry, not fewer.

The biggest threat to the institution of marriage, is not allowing more people to marry, but rather poisoning it in a way that makes more people reject the institution. If de facto relationships seem more appealing, and if we create whole new institutions such as civil unions out of fear, surely we undermine the very institution we claim to want to protect.

Starting in the 1960s, marriage began to be seen as too institutional. It was something your mum and dad did, something for fuddy-duddies, something that conformed for conformity's sake, something at odds with the burgeoning generation of free love.

From the 1970s marriage rates in this country began to fall. In 1971, there were 45.5 marriages per 1000 unmarried New Zealanders; 27,200 Kiwis married that year. By 1987 that had dropped to 25/1000.

In May Statistics New Zealand reported marriages in New Zealand were at a historic low in 2011, with just 11.8 marriages per 1000. That saw just 20, 231 marriages.

At the same time, over 8,500 divorces were granted. Stats NZ said 35% of those who married at the peak in 1971 had since divorced by 2010.

Those numbers tell a stark story – we ain't preserving marriage as it stands. Maybe the gay community is the new growth market we need.

Without being flippant, if we want marriage to remain core to the way we build a stable society, encourage long-term loving relationships and nurture families, then we should encourage everyone to embrace it. If we value people sticking together through the joys and hardships, births, mortgages, deaths and long Christmas lunches, then surely we value everyone in a long-term relationship making their vows and getting wed.

I'm not saying that people in de facto relationships or civil unions are any less in love or less committed; but I think that all other things being equal, people who marry are more likely to hang together through the inevitable tough times in life than those who don't. There's something about the communal, public and solemn aspect of marriage that typically – although not exclusively – adds an extra layer of glue.

And that's without even addressing the rights aspect of this debate. Certainly those who say they want to protect the institution have rights, but it's hard to make an argument that gay marriage causes such harm to them or society that their rights should take precedence over those gays who wish to marry.

Having said that, I don't think such an ancient and pivotal institution should be changed without serious consideration. While I am anti-referenda in most cases, I confess some sympathy for the call for a referendum on marriage, not least to give New Zealanders a more direct voice on a tradition that goes beyond and predates parliament and its laws. Marriage as a custom goes back to before recorded history, so does not merely belong to the law-makers, but is a public institution -- and a public morality -- that belongs to the entire community.

At the very least, our democratic representatives should take great care to consult not just their consciences, but their constituents. Parliament rightly controls our laws, but our customs are not its alone to mould.

I'm also wary of the quickness and brutality with which some are judging the critics of this bill. Colin Craig and his allies, I believe, are on the wrong side of this bill and the wrong side of history. But condemning him for saying that genetics are not the sole determinant of sexuality is unfair and unhelpful.

Let me be clear: I have no doubt gay people are born gay. I don't expect those people to repress their sexuality for the sake of religion, custom or anyone else's personal comfort. They should relish their God-given orientation.

But if, for lack of more precise language, we are all somewhere on the sexuality spectrum, isn't it reasonable to assert that some people have an element of choice in their sexuality?

Some won't like to hear this, but take the example of a bi-sexual who happens to fall in love with one particular person and chooses to be faithful to them. Or the victim of child abuse or rape who may reject sex altogether or become more experimental in their sex life as a result of trauma.

I suspect Craig and I would disagree sharply on the question of degree (I think we're talking very small numbers and for most it's just following your God-given orientation). And just because a few people might have more choice over who they marry, doesn't mean all those other gay people shouldn't be able to wed like crazy. But I'm uncomfortable with the mockery of what were clearly some rather carefully chosen words.

In large part the debate has been civil thus far, which is to the credit of those involved. This is where Kiwi she'll-be-right pragmatism can be at its best.

But let's not get sucked into believeing that this is a battle between those who want to preserve marriage and those who want to overhaul it. the truth is that in this case the two can go hand-in-hand.