Roger Corbett. These old white males who never die, are constantly promoted and ever willing to defend their privileges in calm, whiskered tones. If this were England, he'd have been made Lord Biggles-Pudding long ago. There he was on 7.30, exposing with unconscious blitheness the full truth of the reasons why The Gays can't have marriage. He'd been called up as token Business Leader for the No Case, and appears to have taken his talking points from www.someofmybestfriendsare.com. He deserves full credit for laying bare, finally, what we're really talking about here. It isn't Safe Schools. "Well, first of all, I would like to say that I have many gay friends." Oh ho, here we go, I thought. Get out the popcorn. And he was off. Gays "have a perfect right to a union that is exactly equal and should be treated exactly equally in the community". But not marriage. Marriage is "based on the Judeo-Christian tradition", which makes sense if you ignore the 75% of Australian weddings which are civil, nonreligious affairs, and the weddings of religions that are distinctly not Judeo-Christian. Then we got the "it's about the children" piece, because only married people can have kids and you can't plug an iPhone 4 into an iPhone 7 charger, etc. So far, Roger was following the approved script and maintaining the calm, self-righteous smile of the Jesus-blessed advocate for exclusion. Then Leigh Sales asked him why it was OK for him to speak out but not Qantas CEO Alan Joyce, and Roger went off-piste.

Corbett, for whatever reason, decided to answer this question with reference to slavery. For businesses to speak against slavery, he argued, "I would think that that was entirely appropriate". But marriage is different, it's a "norm" of "being between a man and a woman".

"People deeply believe that. It's not discriminatory in any way. It's a statement that is between men and women."

The alarm bells were going off now at No HQ, but Roger hadn't yet seen the trap he was so confidently laying for himself. On he ploughed: "A man and a woman can have a similar relationship, but it's different. A black man and a white man are equal, but they're clearly different. A black man will never be a white man and vice versa."

Oh. My. God. I'm sure Roger and I were in sync at that moment. I said it quite loudly and scared the dog, while somewhere, deep in the recesses of his mind, Roger was registering that he'd just blown the gaff wide open.

The justification for denying equal marriage rights to LGBTI people, you see, is an old, old sociological theory, one you don't hear expounded these days outside a One Nation rally. Thanks, Roger, now we know.

The theory is "Separate but Equal". It held sway over Western political and legal thought for a solid century in the post-slavery era, from roughly the 1860s to the 1960s. Both the UK (after abolishing slavery in 1833) and the US (which emancipated the slaves in 1863), having accepted, in principle, that all men are created equal, Western philosophy moved on quickly to contemplate the consequences of theoretical equality between the races in a world that remained intransigently racist.

The doctrine of "separate but equal" was one of the manifestations of this conflicted thinking. It led ultimately to apartheid after a detour through eugenics and the Holocaust, and is certainly still far from eradicated (see: Myanmar, right now). An early product was the legally imposed practical segregation of blacks and whites throughout the Southern States via the Jim Crow laws (substantially replicated in Australia too, but we don't talk about that here).

On June 7 ,1892, Homer Plessy bought a first-class ticket on the East Louisiana Railway and sat himself in a "whites only" carriage. He was ejected, arrested and convicted of a crime under Louisiana law.

Plessy appealed his case to the US Supreme Court, where he asserted that he "was seveneighths Caucasian and one-eighth African blood; that the mixture of colored blood was not discernible in him; and that he was entitled to every right, privilege, and immunity secured to citizens of the United States of the white race."

He lost. The court ruled that the Louisiana law, which mandated railways have separate white and coloured carriages, was not unconstitutional. And Plessy was, by Louisiana law, a coloured man. In doing so, the court had a lot of Roger-like things to say. Bear in mind, this was 1896.

"A statute which implies merely a legal distinction between the white and colored races -- a distinction which is founded in the color of the two races, and which must always exist so long as white men are distinguished from the other race by color -- has no tendency to destroy the legal equality of the two races."

And again: "Laws permitting, and even requiring, their separation, in places where they are liable to be brought into contact, do not necessarily imply the inferiority of either race to the other ... The most common instance of this is connected with the establishment of separate schools for white and colored children."

"Laws forbidding the intermarriage of the two races ... have been universally recognised" as valid, noted the Court.

So, concluded the Court, "the underlying fallacy" of Plessy's case lay "in the assumption that the enforced separation of the two races stamps the colored race with a badge of inferiority. If this be so, it is ... solely because the colored race chooses to put that construction upon it."

Plessy v Ferguson remained the law in the US until the 1960s. The Supreme Court's guiding philosophy, that the races were equal but could legitimately be subjected to open discrimination on racial grounds, is partially reflected 121 years later in Roger's averment that "a black man and a white man are equal, but they're clearly different".

There are only two problems with the separate but equal philosophy: it is abjectly immoral and inhuman; and it's 100% rolled gold bullshit.

The Supreme Court noted in passing the difficulty of classification in reality: some US states at the time counted anyone with "any visible admixture of black blood" as coloured; others required a "preponderance of blood" and still others that "the predominance of white blood" must be threequarters if you wanted not to be coloured.

Roger, by his own admission, sees the world in black and white; man and woman; gay and straight. As if we can be neatly classified in binary terms, always acknowledging that we're totes equal but allowing us different legal rights in accordance with the unique characteristics which universally apply to our classification.

A black man cannot ever be a white man. I wonder what my multi-racial children might be allowed to aspire to be in Roger's world.

If you are LGBTI today, Roger will deny you marriage: you're equal, but different. If you were female in 1900, a similar philosophy was used to deny you the vote: you were equal, but different. If you were black -- or, rather, by Roger's determination, not white -- 50 years ago, well-to-do white folks would have denied you entry to their carriage.

All with a calm, comforting, empathic smile. He has many gay friends, after all. They're equal to him. But different.