To explain why, I first need to say something about how the Marriage Act 1955 works.
Any couple wanting to marry must get a licence from a registrar, who is a government employee. In order to do so, they simply need to meet the general statutory rules on who can marry (such as age, not already being married, etc).
Then, once that couple has a licence, they must actually get married. A registrar can do this, but so can a "marriage celebrant".
Certain religious groups that are recognised under the Marriage Act may then effectively appoint their own marriage celebrants. So, provided a couple has their licence, these religious groups can conduct the formalities needed to legally marry that couple according to their own doctrinal beliefs.
In this way, the Marriage Act recognises a division between the State and individual religious groups. The State licences everyone to wed, and actually marries those couples who prefer to do so before a registrar.
However, religious groups also may marry any couples that they choose to, according to the dictates of their particular beliefs.
And this division is made clear in section 29 of the Marriage Act, which states that a marriage celebrant can marry someone once they have obtained a marriage licence, but does not have to do so.
Why, then, are some religious groups worried that they may be required to conduct same sex marriages if this bill passes? Well, since 1955 our law has developed in what may be called a "pro-rights" fashion.
In particular, the passage of the Human Rights Act 1993 has made it unlawful to discriminate against people in certain areas of life on the basis of "prohibited grounds of discrimination".
One of these prohibited grounds of discrimination is sexual orientation.
So the fear is that if same sex couples gain the legal right to marry, then the Human Rights Act may deem a religious group's refusal to actually marry them to be unlawful.
I think that this fear is misplaced, for three reasons.
First of all, there are rights on both sides of the argument here. Religious groups also enjoy the guaranteed right to hold and manifest their beliefs, including their beliefs about who should and should not be married.
So forcing a religious group to perform a marriage that conflicts with their beliefs would breach their rights. Meaning that there needs to be some balancing between the respective rights of religious groups and same sex couples.
Second, that balancing between rights must take place within the structure of the Marriage Act, which is the governing law. And, as I have explained, this legislation deliberately distinguishes between the civil requirements for marriage and religious beliefs about it.
The former are the responsibility of the State, which sets general restrictions on who may get married and marries those couples that wish to have a purely civil ceremony. The latter are the responsibility of the individual religious groups that appoint marriage celebrants and conduct the appropriate ceremonies.
So any claim that says if the State lets a couple marry, then a religious group must actually marry them is completely at odds with the entire approach of the Marriage Act.
Finally, whilst religious groups may be focused on the perceived threat that same sex marriage poses to their beliefs, the consequences of their (and the Law Society's) arguments actually are much greater.
If it would be unlawful for religious groups to refuse to marry a couple based on one of the Human Rights Act prohibited grounds of discrimination, then it is unlawful for them to do so based on any of them. And the prohibited groups of discrimination include things like marital status, religious belief and ethical belief.
That would mean that the Catholic Church is acting unlawfully by refusing to marry divorced people. Doing so is a form of discrimination based on marital status.
And it would mean that an Imam who refuses to marry a Christian couple is acting unlawfully.
That is discrimination based on religious belief.
In fact, any conceivable reason that a religious group might have for refusing to marry any couple at all would most likely be unlawful as it would involve a prohibited ground of discrimination.
This is a clearly absurd conclusion. And while the law may sometimes seem to be a bit silly, a legal argument that produces such an absurd conclusion is usually wrong.
So, here is my message to any religious group that believes it might one day be forced to marry same sex couples. If this is true, then you already have a far, far bigger problem on your hands.
Andrew Geddis is professor of law at Otago University.
Debate on this article is now closed.</i>