Former High Court justice Michael Kirby says a plebiscite on same-sex marriage will create a dangerous political precedent in Australia where MPs avoid making decisions on controversial issues, instead opting for unnecessary and expensive popular votes.
The government is expected to try to pass enabling legislation for a nationwide plebiscite in coming weeks, before a possible vote in February asking Australians if they agree people of the same sex should be allowed to marry.
But Justice Kirby, who served at the High Court from 1996 until 2009, said plebiscite votes were "alien" to Australia's system of representative democracy and the campaign would drive hatred and abuse towards gay and lesbian Australians.
He said Australian voters had rarely supported referendum questions and there was no reason a plebiscite would be any different.
"It will mean any time that there is something that is controversial, that's difficult for the parliamentarians to address or they don't want to address, they'll send it out to a plebiscite.
"I think that's a very bad way. Our Parliament, our parliamentary institutions in Australia and elsewhere are really not working all that well at the moment and what we should be doing is strengthening Parliament and ensuring it gets on with the job," Justice Kirby told ABC radio.
"It's time Parliament did address itself to the issue of marriage equality and giving it out to a plebiscite is simply an endeavour to delay or defeat the measure.
"It hasn't been done by friends to equality."
The Western Australian government has warned the possible February timing would be a distraction a month before voters go to the polls in the state election, but the federal government says it is based on advice from the Australian Electoral Commission.
Justice Kirby – who has lived with his partner Johan van Vloten for 47 years – said Britain's Brexit vote had showed unexpected outcomes were possible.
"This is going to be, if it goes ahead ... running out the old issues of hatreds and animosities, abominations and all the old arguments against gay people.
"We didn't do this for the Aboriginal people when we moved to give equality in law to them, we didn't do it when we dismantled the White Australia policy ... we didn't do it in advances on women's equality, we didn't do it most recently on disability equality.
"Why are we now picking out the LGBT, the gay community? It's simply an instance of hate and dislike, hostility to a small minority in our population. It's unAustralian."
Communications Minister Mitch Fifield said the government hadn't broken a promise to hold the plebiscite in 2016 but AEC advice had strongly recommend against a vote this year.
"We always said it would be held as soon as possible, so our commitment hasn't changed," he said.
"We always said when talking about this commitment, that we would want to do it as soon as possible, as soon as practicable, as soon as we can, also recognising that legislation would always first need to pass the Parliament," he said.