Prime Minister Tony Abbott’s sister Christine Forster has been confronted on live national television by a vocal opponent of same-sex marriage.

As a guest on ABC’s Q&A panel on Monday night, Ms Forster – the openly gay sister of the PM – was interrupted repeatedly by a member of the audience, who claimed gay marriage would hurt “innocent children”.

Ms Forster wants to marry her female partner and has been vocal in her fight for a change to the Marriage Act.

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Questions were fired without notice from one audience member. Photo: ABC

The audience member was not miked and so her questions were only audible to the studio audience. But she did make some provocative comments on the nature of child-rearing.

“What about the innocent children you don’t give a choice to? What about them?” the woman asked.

“Nature is the mother and a father. No scientific, nothing can change that. Nothing. It is a mother and a father. Always has been, always will be.”

Ms Forster, a mother to four and in a relationship with another mother of two, replied: “The important thing I think about children and families is that they are in loving, supportive families.

“And with all due respect, I don’t think that is the exclusive preserve of the traditional family unit,” Ms Forster said to cheers and applause from the audience.

“I think children can be loved, supported and brought to their fullest potential with the most wonderful self-esteem and self-confidence and ability to make the most of themselves in same-sex families and in single-parent families.”

.@philipruddockmp still supports the party position @resourcefultype thinks it’s a political football #QandA http://t.co/EWoIQfnh6z

— ABC Q&A (@QandA) June 8, 2015

Another panel member, African-American academic, activist and poet Dr Cornel West, reminded the inquisitor that “I’m sure that there have been cakes sold to gangsters who are getting married”.

“If that’s true, you have to follow through on the logic of your discriminatory orientation. That’s the question you have to wrestle with in the precincts of your own conscience.”

Dr Cornel West speaking in 2002 to a conference of black scholars. Photo: AAP

The panel moved on to the government’s proposal to strip Australian terrorists of citizenship.

The American experience has shed some light on Australia’s discussion of removing citizenship from Australians who can find another country to live in, but commit acts of terror.

Dr West appeared to have the moral high ground when he gave a history lesson.

“I come from the people who did have their passport taken away, who did have their citizenship taken away because they were defined as un-American, which is to say they were in love with black people,” he said, raising experiences in America during another era.

Philip Ruddock, a Howard-era immigration minister, had just finished explaining that given Australia’s incredible history of migration, about half of the country could be sent to foreign shores by Immigration Minister Peter Dutton, because so many have a parent from overseas.

“There are those people born in Australia and have one parent overseas born. That gets to 50 per cent. Almost a majority,” he said.

.@CornelWest queries @philipruddockmp on the person making the decisions to strip citizenship #QandA http://t.co/5WJpnLaWbd

— ABC Q&A (@QandA) June 8, 2015

On the other side of the panel, another American Bates Gill, foreign policy expert and CEO of the US Studies Centre, enlightened the Australian audience with some home-grown experience.

He likened the citizenship rules to the death penalty, perhaps not because of outcomes but certainly in the enactment of the laws.

“It is like the death penalty in the US, how can you be sure you got it right? We all know governments aren’t great at making smart decisions all the time,” Mr Gill said.

“Some innocent is going to suffer under this type of rule.”