A friend recently asked me to take a look at this FAQ and basically rebut it. I agreed, and I'm doing so, but my discovery of some fairly thorough rebuttals already written has freed me from any need to respond to every paragraph. Here's the (comparatively) short version - I'll link two more-thorough treatments (by other people) at the bottom.
1. What is marriage, in human history?
Throughout history, marriage has traditionally been an institution in which one man owned one or more women. Equality for wives is a modern concept - it is obscene to speak of marriage as being "important for the protection of the pregnant woman", given that (for instance) rape within marriage only began to be outlawed in Australia in 1981. Anyone who wants to talk about the "traditional meaning of marriage" should first learn what that traditional meaning is, and then (hopefully) shut up and give thanks that the institution has changed over time. This applies also to the later bit about how marriage "helps protect women from exploitation". Note also that no-fault divorce is a very recent concept, at least in Australia.
It's also worth noting that the bit about "the passionately patient love and labour of both their mother and their father" is sharply at odds with large parts of history in which children were raised largely by servants and rarely saw their parents. Technically this is mentioned in regard to "infants" - humans are only "infants" for a few years, however, and beyond infancy there are plenty of historical examples of children routinely taken away from their families to be raised communally by some social institution (often the army).
2. But isn’t marriage about ‘love and commitment’, not about gender?
-The "continuation of human life" is hardly an issue here - we are at risk from overpopulation, not underpopulation.
-"Natural sexual attraction between man and woman" implies that same-sex sexual attraction is unnatural. On the contrary, homosexual behaviour has been observed in (at last count) approximately 1500 species.
-Marriage is an exclusive commitment. This is somehow overlooked in the FAQ.
-Note the manipulative language used - Andrew Sullivan is a "prominent homosexual advocate", whereas David Blankenhorn is a "marriage expert".
-It is true that same-sex couples "cannot naturally give rise to children". For heterosexual couples, the state does not care whether children are the result of sexual intercourse, IVF or adoption. If the state cares about these things for homosexual couples, then that is simple discrimination.
3. Aren’t we discriminating against homosexual people?
Yes. "Separate but equal" is not equal. This is not new.
the ‘right to marriage’ infringes on the still greater right of the child to have both a mother and father
There is no such right of the child. If there were, adoption by single parents would not be legal. It is legal, and the groups fighting against same-sex marriage don't seem to have a problem with it.
Only the natural union of a man and a woman can create children
This is factually incorrect, and incidentally overlooks adoption.
This attention is to encourage parents to remain together and with their children, to avoid the breakdown of a family unit and its resulting disadvantage to children
If the state is so opposed to "the breakdown of a family unit", why did Australia introduce no-fault divorce in 1975?
4. Does a child need both a mum & a dad?
...a government should never be complicit in having children planned to be deliberately placed in a home without their mother or father– by the legalisation of same-sex marriage, same-sex adoption and same-sex surrogacy
Somehow there doesn't seem to be any objection to adoption by a single parent.
The argument resting on the UN Declaration on the Rights of the Child is false, because such an interpretation would outlaw adoption entirely.
5. How common is homosexuality?
The research cited is cherrypicked, and the data presented from it is also cherrypicked. Even the publicly-available abstract of this carefully-chosen paper notes that "some same-sex attraction or experience was reported by 8.6% of men and 15.1% of women", which is significantly higher than the quoted figures of 1.6% and 0.8% for those identifying as homosexual. The "long-discredited survey of criminals by Kinsey" (note once more the loaded terminology) was indeed criticised upon release, but has since been verified by, among other things, removing the data from current or former prison inmates (who had constituted 25% of the original sample) and male prostitutes (5%). Furthermore, Kinsey's 10% figure refers to the "completely homosexual" category in a 7-category scale (as opposed to the popular 3-category scale of heterosexual/bisexual/homosexual).
The above demonstrates wilful deception by the authors of this FAQ, but is otherwise irrelevant. Even small minorities have rights, and fewer homosexual people means less potential damage to society if they are allowed to marry. The important point is civil rights, though - I would call this tyranny of the majority, except that the majority of Australians actually supports same-sex marriage.
6. People are born gay, right?
Uncertain, unlikely to have a simple answer, and in any case irrelevant. A man does not choose to fall in love with another man, any more than I (a straight man) choose to fall in love with a woman. Sexual orientation is a complex phenomenon which we don't well understand, and it can change over time, but it is not a choice.
7. But don't we need to reduce gay-bullying?
Indeed. Whilever authorities discriminate against gay people, how can children be expected not to do so? Recent educational initiatives are helpful in educating children, but more so in forcing school administrations to treat homosexual students fairly.
homosexualising the sexual instruction of our children at school
Homosexuality is not a communicable disease. God forbid that our children should learn tolerance and respect for others.
8. How else will “gay marriage” harm society?
It is true that extra rights recognised for a certain group means that I am no longer allowed to violate those rights. I have no problem with this, personally. the example about "hate speech" is a blatant straw man; many groups have "special" rights, and yet it is still legal to speak about them "in a negative light".
Where same-sex marriage has been legalised, there have been all sorts of unwanted repercussion on the rest of society.
The repercussions mentioned all seem to be in America, a Christian-dominated country with some very wealthy religious organisations fighting against gay rights - I do not accept those stories at face value, particularly since they sound very much like just another aspect of the religious war against sex education in the USA. Elsewhere (eg. in Canada and the Netherlands), same-sex marriage appears not to have made much difference to society.
9. Should a child ideally have both a mum and a dad?
One Adelaide paediatrician opposes same-sex couples as parents, and incidentally conflates "gay and lesbian parenting" with "when families fracture". As above, this concern for broken homes and lack of a father/mother seem odd when adoption by single parents is accepted.
The quote from the American College of Pediatricians struck me as strange - "an association of hundreds of paediatricians in the US"? The American College of Pediatricians is a socially conservative breakaway group, formed in 2002 in protest against the major body's support for adoption by gay couples. It has an estimated 60-200 members. The major professional body in the USA is the American Academy of Pediatrics; formed in 1935, it has approximately 60,000 members (that is, 500-1000x the membership of the breakaway group). The major body supports parenting by same-sex couples.
However, nobody needs to resort to “the best available science” to defend the obvious insight that a little child needs both a mother and a father. The judgment of anyone who cannot see this as a self-evident fact of life, as the most primal and necessary condition of a child’s wellbeing, is suspect.
This final statement betrays (once more) a stunning ignorance of history. Historically children have routinely been raised with little to no contact with their fathers, and even without much contact with their mothers. Witness wet-nurses, nurses, governesses and the like.
It's amazing how many "self-evident facts of life" have turned out to be cloaks for bigotry of one kind or another, notably racism and sexism. It is my opinion that this is no exception.
The above is not intended as a complete or well-referenced argument. I think it suffices anyway, but better arguments have been made by others. Here are two which I find particularly good.
Australian Marriage Equality - Answering the Critics
Bidstrup on marriage