So just when I think I've got my spiel about being a gay marriage agnostic down pat, Macklemore and Bruni come along and shake the foundations of my unknowingness. Thirteen months ago I wrote a column in a national newspaper backing same-sex civil unions, but saying I was undecided on legalising gay marriage. What made my stance awkward was my background as an atheist Labor voter, who has lived in sin and abhors the pain homosexuals suffer trying to be treated fairly. I am supposed to back gay marriage. But my argument was that we need a marriage ideal that reflects social norms and biological reality. It should be built on the intention to make a genetic investment - having children - because that creates a hot-wired incentive for adults to stick together and cede their rights to those of the young 'uns. The outcome, in an ideal world, is family units based on more than fleeting love. The hope is you get a stronger, stable, selfless, child-focused society that nonetheless accepts and supports same-sex civil unions, single parenthood and childless families without holding them up as the default model. We can argue about that theory forever. I thrash it out in my head every day and see the myriad flaws. That's why I am undecided.

But can someone quickly change their mind on something so steeped in principle? I'd love to say yes, because it's hard justifying gay marriage agnosticism, especially to kids. Barack Obama changed his mind quickly enough. His inaugural address in January equated gay rights and the black civil rights movement of the 1960s by invoking Stonewall, the scene of gay rights riots in New York in 1969. Julia Gillard has barely six months to change her mind if she's to bow to pressure to back gay marriage before she departs The Lodge. I've been secretly hoping for an epiphany to make up my mind for me. The other day I saw a father sitting on a bench with a baby. Both were clearly deeply in love. Was he a gay father? I hoped so. I thrash it out in my head every day and see the myriad flaws. That's why I am undecided. I drive around listening to Macklemore's Same Love: ''I can't change/Even if I tried/Even if I wanted to''. It is so beautiful you can't help but sing out loud at traffic lights and embarrass your son and almost swallow the ''gay marriage equals civil rights'' mantra.

And Bruni's passage just cuts to the core. ''Who and what am I defending if there's no injured party under legalised homosexual marriage, especially if no one loses except those who strongly oppose it?'' As the US Supreme Court hears arguments on California's Proposition 8 and the Defence of Marriage Act this week, the gay Bruni is among many commentators who think legalised gay marriage is inevitable anyway. Some conservatives are fighting back against what they call the ''myth of inevitability'' and are marching outside court. Their soulmates are marching in Paris and London, too, while New Zealand opinion polls show a backlash against MPs as they prepare for a third, deciding vote to back marriage equality. But other conservatives have succumbed. Former George W. Bush political strategist Karl Rove has even said he could imagine a pro-gay marriage Republican candidate for the presidency in 2016.

The young 'uns don't get why old parents like me are so confused. The gay lobby and lefties don't get why Gillard backs traditional marriage either. They hold out hope a softening Tony Abbott may take heed of his sister's homosexuality. My conscience says male-female marriage should remain the biologically realistic, child-centric ideal to which society should aspire; a role model for the young who need to get the message and put into practice my ideal world. Problem is, the young 'uns are not listening much. Perhaps that is a credit to every parent who has taught their kids to treat everyone fairly and decently; not to judge people by lifestyle or sexual preference; and to accept the equal right of all to make choices and not be targeted by government. Perhaps parents like me are more the problem than the solution. Such is life …

astokes@fairfaxmedia.com.au