Gaita believes that there are people who oppose homosexual marriage because they find gay sex disgusting or immoral or because they believe it will have damaging social consequences. But he sees these objections as being relatively superficial.
The most radical source of opposition to homosexual marriage, he argues, is that many people don't believe that there is depth in homosexuality: that it is not deep enough to be integrated into the meaning of marriage. That leaves the term "homosexual marriage" as an oxymoron and, if true, it would mean that if homosexual marriage were legalised the concept of marriage would be degraded:
From this perspective, even if the law were to permit gay marriages, these would be marriages in inverted commas only. The state cannot do what is, so to speak, conceptually impossible. If it were to try, this thought continues, it would degrade the concept of marriage. After a time, even heterosexual married couples would no longer understand what it means to be married.
But Gaita is strongly opposed to this view of homosexuality; he believes that society should recognise the "depth and dignity" of the "sexual being" of homosexuals as,
Our sense of a common humanity is premised on seeing in all human beings their capacity to make meaning that we respect of the big facts that define the human condition - our mortality, our vulnerability to misfortune and, of course, our sexuality. To be blind to that in others is to be partially blind to their humanity.
That's a significant quote. He is arguing that our common humanity rests on our capacity to make our own meaning of who we are. Therefore, runs the argument, if we don't respect how others make meaning we are denying them human status. Homosexuals are just doing the human thing, claims Gaita, of defining their own being in ways that are meaningful to them, so not to recognise what they decide to be would be a denial of their full humanity:
Laws premised on blindness to the full humanity of our fellow citizens wrong them more profoundly than can be conveyed by the complaint that they deny them access to goods and opportunities.
Gaita's position is not original. It's another way of putting the orthodox liberal view. And it is not obviously true. Why should we accept that it is our capacity to self-define our place in the world and our being which is the measure of our humanity?
There was an older view in Western philosophy that our being flowed from our essence, which in turn then provided our "telos" (the end toward which we are rightly oriented).
I'm not sure the ancients adequately defined this essence, but even so it strikes me as a more promising philosophical framework than the modernist liberal one.
A core problem with the modern view is that we are supposed to accept that meaning is something we make for ourselves - which leaves meaning as something subjective and therefore not very meaningful. It doesn't really seem to matter in the liberal view what specifically men choose to do or be, as there is not thought to be a masculine essence which helps to define our ideal being and the fulfilment of who we are.
And so liberal moderns have no basis for preferring one concept of being and self to another, as their concept of being doesn't connect to anything beyond the individual self. It doesn't matter, in this view, whether I choose to be a self-sacrificing father, a juggalo or a brony. These are all the same, and must be treated the same, as they are all instances of individuals defining their own being in ways that are meaningful to them. If anything, it is the fatherhood option which might be ranked lower by liberal moderns, as it might be thought to have been accepted for reasons of tradition rather than as something individually self-defined.
If it's true, as liberal moderns claim, that what matters (what makes us fully human) is our capacity to make meaning for ourselves of our own being, then value will shift away from what we specifically choose to do or be, and flow instead to the idea that we must accept as equal each individual's self-made being - as to judge differently would mean denying to some individuals what makes them human.
And so value for liberal moderns resides in "equality", "tolerance", "respect", "non-judgementalism", "diversity" "non-discrimination" and so on. But these values circle round an emptiness - they exist to uphold the idea that there is no being except the one we make for ourselves, that there are no real standards of what we choose to do to be, that there are no given qualities to who we are which place us naturally within families or communities or larger human traditions, and that meaning is ultimately subjective and, therefore, not very meaningful.