The controversy surrounding gay marriage has now reached a fever pitch in countries like Australia and the UK, as governments have begun to move past debate and towards legislative change.
Those resisting the change - mostly, but not entirely, religious people - argue that the issue is being framed in the wrong way.
For them it is not a matter of extending the right, nor the teleological good, of marriage to gay people, but rather of redefining the very thing in which marriage consists.
For centuries - indeed, for millennia - they argue, marriage has been understood as a conjugal relation between men and women linked to the natural bearing of children.
Thus there is something monstrous about the state even claiming to have the power by law to change the definition of a natural and cultural reality which has historically preceded the existence of the state itself.
Opponents also point out that neither the United Nations nor the European Union regard homosexual marriage as a human right; rather, it is seen as a matter that must be left to the judgment of civil law and, by implication, to local cultural consensus.
Since a right to enter into heterosexual marriage - "international law" - recognises something specific about heterosexual union.
The implication here is that to deny gays the right to marry is not to infringe their rights as human beings, because the right to marry only applies to human beings insofar as they are male and female.
By analogy the right to a pension may be universal, but applies only to people over a certain age.
International law, meanwhile, remains somewhat more agnostic as to whether the right to marry might be extended to gay people. Historically, the very idea of marriage has been shaped by public recognition of heterosexual practice.