A debate about marriage equality derailed a Liberal Party event in Murray Bridge on Friday night.
Local resident Michael Collins, who is in a committed relationship with another man, confronted Senator Cory Bernardi about his conservative views.
"I'm normally fairly mild-mannered, but I find it insulting Senator Bernardi wants to treat my family like second-class citizens," he said.
"Marriage should be between two people."
He said the Liberals’ proposed plebiscite on marriage equality was an example of good intentions producing a terrible outcome.
Senator Bernardi said he would not redefine an institution that had stood for many years – "like apartheid?" Mr Collins interrupted – nor surrender to the logic used by same-sex marriage advocates.
"The same arguments are employed by people who say 'I want to marry more than one person'," Senator Bernardi said.
"I'm being logical and consistent.
"Marriage is not a human right – look at the UN charter, it's not there."
He also asked why there had been such an outcry about "newfound discrimination that hasn't existed for thousands of years".
He suggested Mr Collins register his relationship with state authorities to ensure he and his partner could enjoy the same legal rights as a married or de facto couple.
However, no such register exists in South Australia.
The confrontation occurred at a community forum featuring Senators Bernardi, Anne Ruston and David Fawcett and candidate Kerrynne Liddle.
The future of the River Murray, Lower Lakes and Coorong was the topic most often brought up by audience members.
Senator Ruston assured those present that Agriculture Minister Barnaby Joyce had "the best interests of Australia" at heart.
She said the proposed removal of the barrages on Lake Alexandrina was "not going to happen", though an upgrade was likely "if the South Australian government said it was a high priority".
If given the option, she said, she would also support a connector between Lake Albert and the Coorong to reduce salinity.