Most responses to Kevin Rudd's conversion on same-sex marriage have inevitably focused on whether it will change Australia's political dynamic on the issue. Equally predictably, more cynical members of the commentariat have chosen to see Rudd's announcement as his latest round of jousting with the woman who deposed him as prime minister.
Well, yes. Rudd's addition to the ranks of those advocating a change in the law is a reminder, if one were needed, that by opposing same-sex marriage Julia Gillard and Tony Abbott are adhering to the view of a shrinking minority of the Australian community. Polls regularly indicate that more than 60 per cent of voters now favour change, with support rising to more than 80 per cent among those aged 18–24.
The momentum is almost certainly irreversible, and the question is not whether, but when, there will be legal equality for same-sex relationships, including the right to use the 'm'-word.
On this issue, the prime minister and the opposition leader have, to use the apt if cliched phrase chosen by Greens Senator Sarah Hanson-Young, placed themselves on the wrong side of history.
That's the politics. Those who bother to read the lengthy blog entry in which Rudd announced his change of heart, however, will be drawn into a broader debate about the relationship between church and state, a debate of a kind that takes place too rarely in Australian politics.
We are familiar with sloganeering — from partisans of both church and state — about what that relationship should be, and with the invective that gets hurled whenever legislation is mooted on issues such as reproductive medicine or the hiring policies of church institutions.
But Rudd's argument does not descend to slogans or invective, and may profoundly discomfit those who think civilisation will somehow be imperilled if church teaching on marriage and family is not enshrined in secular law.
Rudd accepts the traditional Christian understanding of sacramental marriage as an exclusive relationship of one man and one woman, and insists that a change in the law should not impose on religious institutions any alteration in their own practice. But he argues that the churches' teaching and practice can and should coexist with a secular law that acknowledges same-sex as well as heterosexual marriage, and with various models of parenting — heterosexual, same-sex, and single-sex.
These assertions should not even be contentious. The Catholic Church has always taught that marriage is a natural institution, properly regulated by civil law, and that not every natural marriage is necessarily a sacramental marriage. Rudd is essentially saying little more than that, or more precisely, he is drawing out the implications of a distinction between natural and sacramental marriage for living in a secular, pluralist society.
In earlier societies, shaped by a more or less uniform profession of Christianity, the natural/sacramental distinction may have been a notional one. In the secular societies of the modern West, however, the distinction has become a practical challenge: we should live by it if we do not seek to impose our faith on others.
Nonetheless the argument Rudd is making is contentious to many adherents of Australia's various faith traditions, and among the clerical leadership of the Catholic Church in particular.
Conceding the reality of same-sex relationships, they may accept 'civil unions' but baulk at describing any but a heterosexual union as 'marriage'. Asked why not, the usual response is that if the legal definition of marriage is broadened to include same-sex unions the heterosexual family would be undermined.
It is never explained just how that would happen, nor is it acknowledged that the horse has bolted long ago: there are many different kinds of family in modern Western societies, some with heterosexual parents and some with same-sex parents, but there is no evidence that children being raised by the latter are therefore growing up as deficient human beings.
Why are so many of the churches' leaders afraid of accepting the consequences of living in a pluralist society? Why is the tolerance they all publicly profess too often belied by the expectations they have of the state?
There is a long tradition of theological reflection that acknowledges the autonomy of both church and state. Indeed, it is no accident that modern liberal notions of tolerance emerged first in Western societies grappling with the experience of religious diversity.
It cannot be denied, however, that the Catholic Church came to terms with that diversity slowly and reluctantly. Until the Second Vatican Council, when popes and bishops spoke of 'religious freedom' they typically meant freedom for the church to spread its message.
The council's Declaration on Religious Freedom was substantially the work of an American Jesuit, John Courtney Murray, and it reflected his experience of American liberal pluralism. The declaration did not shrink from proclaiming that freedom was an inherent part of human dignity. It was not a message some people in the church wanted to hear, and to this day those who want to wind back the achievements of the council usually start with the declaration on religious freedom. They will say it has been 'misinterpreted'.
In Australia, one measure of whether Courtney Murray's vision survives, or whether the revisionists have prevailed, may be in the response that Catholic prelates make to Rudd's argument for same-sex marriage.
Ray Cassin is a contributing editor.