The Australian Medical Association and the Australian Psychological Society told Fairfax Media there was no scientific evidence that children of gay and lesbian parents had poorer outcomes than those with heterosexual parents.

Ahead of the upcoming postal survey, conservatives have raised concerns over same-sex parenting, arguing that allowing same-sex marriage would license families they regard as sub-optimal.

Former defence minister and Tony Abbott ally Kevin Andrews used a television interview on Monday to assert "the best environment for raising children" was a family with a mother and a father.

"Overwhelmingly, the social science research points to that being [optimal]," he said. "Children brought up in those circumstances, as a cohort, are better off than those who are not."

But AMA president Michael Gannon, who hosed down a minor internal revolt at the weekend over his organisation's support for same-sex marriage, rebuked the argument and noted parenting was unrelated to the question of marriage laws.

"The issue before the Australian people, before the Australian Parliament, is not about same-sex parenting. That's not even the discussion that is being debated," he said.

Dr Gannon stood by the AMA's statement in May that there was "no putative, peer-reviewed evidence to suggest that children raised in same-sex parented families suffer poorer health or psychosocial outcomes as a direct result of the sexual orientation of their parents or carers".

He dismissed concern from about 400 AMA members who want the AMA to reconsider its position, noting they represented only about 1 per cent of the organisation's 30,000 members.

The Australian Psychological Society, the peak body for psychologists, conducted a literature review in 2007 and concluded outcomes for children of homosexual parents were "on par" with those in heterosexual families.

Since then, one major study using a large random sample - conducted by Mark Regnerus??? at the University of Texas - purported to defy that consensus. However, it was widely discredited when the data was examined by other researchers.

"The analysis was wrong," said Damien Riggs, associate professor of social science at Flinders University and APS fellow. "It is proven that their methods were unsound - the way they did their analysis was unsound."

Dr Riggs said while public debate often made the science appear contested, in the social science community the issue was largely settled.

"There are no noticeable differences between children of heterosexual parents and children of homosexual parents, other than discrimination," he told Fairfax Media. "What we need to do is combat discrimination, so then there are no differences at all."

That view was also backed up by a 2010 meta-analysis of 33 studies of two-parent families, published in the US Journal of Marriage and Family.

Lyle Shelton, a leader of the newly-formed Coalition for Marriage, was widely criticised when his Australian Christian Lobby described the children of same-sex parents as "another stolen generation".

Gay Labor senator Penny Wong took Mr Shelton to task over the remark last week, proudly telling the Senate in a moving speech: "We love our children."

A defiant Mr Shelton defended the analogy on Monday. "We are proposing setting up government policy that requires some children to miss out on their mother and father," he told Sky News.

Tiernan Brady, executive director of the Equality Campaign, said fear of same-sex parenting was one of the "daily red herrings" offered up by opponents of change that had nothing to do with marriage.

"What we're witnessing is the 'no' side already conceding that they cannot win the argument about marriage equality," he said. "They know that the Australian people want it, so they've given up on the issue. That's why they are deliberately trying to deceive."

Fairfax Media contacted the Coalition for Marriage seeking further academic studies on same-sex parenting, but received no response.

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