It is no such thing.
It is simply wrong and misleading to depict the case for same-sex marriage as a case for ending discrimination or for equal legal recognition of relationships. The Federal Parliament amended 84 pieces of legislation after the 2010 election to place homosexual rights and entitlements on the same basis as others. The push for same-sex marriage is therefore largely ideological, because there is clearly no intention in any jurisdiction that they be subjected to any substantial discrimination on entitlement.
Peter van Onselen shortly before Adam Bandt's show and tell argument in Parliament, like Greiner, argued for same-sex marriage as a human right but as is always the case with this assertion never actually demonstrated why it was a human right, choosing instead, typically, to construct a series of pejorative straw men and 'stacking the deck' arguments to hopefully convince us that same-sex marriage was the natural consequence of a long evolutionary development in marriage. Of course, having gone down this path he might have considered a further evolutionary development - the Greens' bill for same-sex marriage still limits marriage to two persons, itself arguably discriminatory to those favouring polygamy or group marriage. How long would we have to wait for that example of discrimination to be addressed?
If a human rights basis is to be developed for same-sex marriage then it is first necessary to determine whether same-sex couples actually qualify for marriage. What is it about marriage that determines who may enter into marriage?
What we can say about marriage is that despite varying cultural expressions, it is seen as the union of a man and a woman who make a permanent and exclusive commitment to each other, of the type that is fulfilled by bearing and rearing children together. This concept of marriage, allowing for variations in customs and ritual, is consistently found across cultures throughout history. Marriage involves a comprehensive union of spouses, with norms of permanence and exclusivity. These combine to create a special link to children, for their sake, that protects their identity and nurture by a mother and father.
It is the link to children that gives marriage its special character.
But why a man and a woman, and not two men or two women?
With one exception a person is complete within themselves as to bodily organs and their functions: heart, lungs, stomach and so on. In other words, to fulfil any of these functions a person does not require a contribution from anyone else. The one biological function for which individual adults are naturally incomplete is sexual reproduction. In sexual intercourse, and no other form of sexual contact, a man's and a woman's bodies are joined by way of their sexual organs for the common biological purpose of reproduction. Their bodies become one, thereby securing future generations at the same time as they are giving unique expression to their love for each other.
Marriage is deeply and uniquely orientated to bearing and nurturing children. Marriage ensures children access to both their mother and father and the security of the love between the parents. It provides for them a role model of human love of the parents relating as man and as woman, and its complementarity also ensures the unilateral love of each parent to the child and the necessary differences between motherly and fatherly love.
The fact that divorce happens, or one spouse dies early, or some couples are infertile and perhaps circumvent that lack to conceive through artificial reproductive technologies, including the use of donor gametes and surrogate mothers, or a couple beyond the years of child bearing marry, does nothing to change the reality of marriage. Same-sex couples simply do not qualify.
At its deepest level, marriage is the union of difference, the combining of a man and a woman to make one flesh, a union that is physical, emotional and as well, mystical.
To the contrary, same-sex marriage would be the union of sameness, with the distinctive and historical orientation towards the bearing and nurture of children dissolved. In its stead is to be offered a view of marriage which places sexual choice and emotional commitment at the centre.
So, let's be clear on this: extending marriage to same-sex couples would represent a radical revision of the public understanding of marriage as a social institution. To go down this path would be for the law to teach that marriage is fundamentally about adults' emotional unions, not complementary bodily union or children. Because there is no reason that primarily emotional unions (any more than ordinary friendships in general) should be permanent, exclusive, or limited to two, these norms of marriage would make less and less sense. Less able to understand the rationale for these marital norms, people would feel less bound to live by them, to their own detriment, and especially to the detriment of children.
According to the newspaper report I began with, the supporters of same-sex marriage claim through the national convener of Australian Marriage Equality, Mr Greenwich, the existence of "an unstoppable momentum for a reform that continues to win hearts and minds in the wider community and the parliament". Well this remains to be seen. To be sure, their efforts will not go unchallenged. Same-sex marriage in law is by no means inevitable.