As of last week, Malta has marriage equality, along with a population that is 98% Roman Catholic. In Australia — 30% “no religion” and on every poll at least 65% in support of marriage equality — the “debate” grinds on. And on.

Turgid is the word that comes to mind, each time I contemplate the disgusting mess that our federal politicians have made of this fundamental question of human decency. To see Liberal MP Tim Wilson explain why he might cross the floor to vote for a private member’s bill for marriage equality, but wouldn’t do so for a Labor bill doing the same thing, really drives home how well this issue exemplifies the amoral abyss Parliament has become.

No, ignore those pathetic wheedlers and their endless political machinations. Let’s talk law. This is the case for marriage equality, and it is undeniable.

What is marriage? Unquestionably, it is a religious institution. Every religion celebrates marriage, with infinitely varying ceremonies, vows, traditions and rules. And, with perhaps a few minor exceptions, they all restrict marriage within their faiths to opposite-gender couples: a man and a woman.

But marriage is also a legal institution. It is formalised in all jurisdictions, and certainly in Australia, under law. A marriage cannot achieve any societal recognition otherwise. Australia’s constitution gave law-making power in respect of marriage to the federal Parliament, and the Marriage Act provides the legal foundation for every marriage in this country.

[Matthewson: what’s a guy gotta do to pass marriage equality around here?]

There’s no difficulty with marriage being both a religious and a legal institution. Each has a different foundation and serves a different purpose. The distinction is critical, because it’s where the arguments against equality meet their defeat.

Those arguments base themselves in religious doctrine. They always boil down to one simple proposition: that marriage is traditionally between a man and a woman, as ordained by scripture. It is, one way or another, dictated by doctrine, and that is that.

I have no argument to make against religious belief. There is no need for anyone to deny another’s principles. There is, however, a need to recognise the ground on which those principles stand.

Imagine you speak for a specific faith, let’s choose the Church of England as a generic representative. Within that church, marriage is recognised and regulated by doctrinal boundaries. It is restricted to opposite-gender couples.

The Church of England recognises its own marriages. It also recognises every other religion’s marriages. If you were married under the Catholic faith, or Islamic, Jewish, Buddhist or Hindu, even if you had a civil ceremony outside religion altogether, the Church of England is fine with that and accords no less respect or acceptance of the validity and sanctity of your marriage than it does its own.

That’s the key. Doctrinally speaking, it makes no sense for any religion to recognise the marriage of any other, especially not civil marriages, because they don’t follow the rules. A marriage made without a nuptial mass conducted by an ordained (male) priest cannot be right in God’s eyes, under Catholic doctrine. So how can it be accepted by the Catholic Church at all?

Religions recognise each other’s marriages because they conform to the legal institution of marriage. It is not the institution of the other religion they are recognising, but the legal institution. It cannot be otherwise. I’m sorry to labour the point, but it is the whole point, and it tends to be overlooked.

Once we appreciate the dual nature of marriage, we can get past all the religious/moral debate. That stuff can carry on within each religion’s domains, along with all their other points of doctrinal contention such as whether a woman can be a priest. It’s nobody else’s business or concern.

Most importantly, it is not the law’s concern. The law relating to marriage is simple and clear. Since 2004, when John Howard pushed through amendments to the Marriage Act without whisper of a plebiscite, the law has expressly limited marriage in Australia to “a man and a woman”.

This law, as it presently stands, conflicts with a fundamental principle of law: equality before the law. This rule goes back to Magna Carta and way beyond; it has precedents in Roman law and ancient Greece. It’s enshrined in article 7 of the Universal Declaration of Human Rights, to which Australia is a signatory: “All are equal before the law and are entitled without any discrimination to equal protection of the law.”

That is not to say that the Marriage Act is not valid law; it is. The High Court had no difficulty confirming that federal Parliament has power to define marriage as it wishes, and the current definition is an available option.

Although a law can be made, that is not to say that it should be made. Legal power is one thing; legal principle is another. Equality is one such principle, and a good law is one that conforms to it unless there is a very good reason why it should not.

To put it simply: equality before the law should always be the default. We should depart from it only for a higher purpose. An example is that children are not treated equally by the law, because we accept that they are incapable of the same level of rational decision-making as adults. Thus we draw the arbitrary line at 18, before which the law says you are unequal.

[Marriage equality postal plebiscite plans are much further along than you think]

The law used to treat women as unequal, as it did indigenous Australians and same-sex couples. Marriage aside, gay couples are now given equal legal rights as everyone else, because we recognised that there was no good reason why that should not be so.

The remaining question is whether marriage should continue to be kept aside. To do so, we need a compelling reason why the law should treat couples who want to marry but who are not opposite-gender differently. What is the justification, recognisable by the law, for maintaining inequality in marriage?

I don’t know of any. Tradition is no basis for upholding inequality; slavery, child labour, genital mutilation and so much more once had the same claim. Everything else is distraction. Sure, let marriage celebrants and church halls exercise their right to discriminate against same-sex couples if they wish; even allow homophobic cake bakers to refuse service for a gay wedding. That’s not a reason for not ending the discrimination that prohibits some people from being married.

Equality before the law should be restored. Marriage should be open to any two people (minors and incestuous couples excluded) who want it. It is as simple as this: replace “a man and a woman” with “two people”. It’s time.

Note: Marque Lawyers has launched a campaign to hasten this change, targeting the Australian legal community. We think it’s also time that lawyers spoke up for the law. Check it out at www.twopeople.org.au.