Former Prime Minister Tony Abbott has warned traditional marriage has always been considered the heart of family and the institution needs to be passed on “undamaged” in a speech to a US conservative Christian organisation.

Mr Abbott told the Alliance Defending Freedom overnight that traditional family was the best social welfare system that mankind has ever devised, quoting John Howard.

“Policy-makers 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,” Mr Abbott said in the speech, reported by The Australian.

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Mr Abbott reflected on the complex structures of families in modern times including his own family tree in which two of his sisters are divorced – one with a new partner and another with a same-sex partner.

“To me, my sisters’ partners are first-class members of our extended family,” he said.

He called for less ideology and more common sense in the marriage equality debate.

Cabinet Minister Christopher Pyne said it was a democracy and Mr Abbott was entitled to express his views.

“Tony Abbott can say whatever he wants to whomever he wants,” Mr Pyne told the Nine Network.

“That’s called freedom of speech.”

Labor frontbencher Anthony Albanese also defended Mr Abbott’s address.

“Tony Abbott can talk to whichever group of right wing nut jobs in the United States he likes, whichever one because there’s lots of them as we’re seeing at the moment with the right wing of politics in the US,” he told the Nine Network.