Same-sex marriage will lead to "erosion of family" values: former Australian PM

Former Australian Prime Minister Tony Abbott will tell a U.S.-based Christian group that same-sex marriage equality will lead to the "erosion of family" and damage the institution for generations to come.

Abbott is due to give a prepared speech to conservative, far-right group Alliance Defending Freedom in New York on Friday (Australian time), but the Australian media has published an advance copy of his address.

The former prime minister, replaced by Malcolm Turnbull in September last year after an inner-party revolt, said Australia - and other places yet to legislate same-sex marriage - should not hastily change the fundamental nature of marriage without mapping out any possible impact on society.

"We shouldn't try to change something without understanding it, without grasping why it is that one man and one woman open to children until just a very few years ago has always been considered the essence of marriage and the heart of family," Abbott said in his speech, quoted by The Australian newspaper on Friday.

"We can't shirk our responsibilities to the future, but let's also respect and appreciate values and institutions that have stood the test of time and pass them on, undamaged, when that's best. That's a goal we should all be able to share."

Despite having a sister who is in an openly homosexual relationship with another woman, Abbott would draw on his own family to reaffirm his stance that the definition of marriage should remain between a man and a woman.

"These days, at least in Western countries, family structures are typically more complex than they used to be," Abbott said.

"Two of my sisters are divorced. One has a new partner. Another has a same-sex partner. To me, my sisters' partners are first-class members of our extended family.

"In today's world, we need less ideology and more common sense; we need less impatience and more respect; we need less shouting at people and more engagement with them."

Currently, same-sex marriage is allowed in all 50 American states after the Supreme Court in June last year ruled that marriage equality was protected in their constitution. Australia is yet to legalize gay marriage, but Prime Minister Turnbull has pledged a plebiscite on the issue in 2017.

Abbott urged those in politics, and the broader public, to first consider the repercussions of changing marriage, saying they could be catastrophic for everyday families.

"Policymakers shouldn't be judgmental about people's personal choices but we can't be indifferent to the erosion of family given its consequences for the wider community," Abbott said.

"It was my distinguished predecessor (Liberal Party PM) John Howard who pointed out that the traditional family was the best social welfare system that mankind has ever devised."

Last week Abbott revealed he would recontest his local seat at the next election, joining Labor's Kevin Rudd, as the only former prime minister to seek another term following demotion from Australia's top job. Enditem