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Mr Turnbull told 2Day FM host Em Rusciano that "hurtful" and "cruel" comments were part of the debate about same-sex marriage ahead of a postal plebiscite on whether to make it legal.
"We're in a democracy, right, and people will often say things that are hurtful and unfair and sometimes cruel, but that is part of a debate," he said.
"The only way to stop people saying things that you find hurtful is to shut down free speech."
He added that he and his wife, Lucy Turnbull, would be both voting Yes.
"Lucy and I have been long supporters of same-sex marriage," Mr Turnbull said.
Ms Rusciano accused the government for conducting a plebiscite, saying it "emboldened people who are anti-homosexual ... to say some awful things".
She said she didn't believe Mr Turnbull was being fair.
"Do you think equality is a debate? Is that something to be debated?
"I don’t think saying 'someone isn't equal to me because of who they love' is a debate or is a legitimate argument. I think it is denying them their rights."
Voters urged to report offensive ads after anti-gay posters surface in Melbourne
Labor has slammed “exceptionally limited” rules covering same-sex marriage postal vote advertisting material and is encouraging Australians to forward hateful campaign material to a special Senate enquiry.
Anti-gay posters and pamphlets have surfaced in the lead-up to the enrolment deadline for the same-sex marriage postal vote, prompting renewed calls for campaign rules.
Letters in a combination of Chinese and English have appeared in Sydney letterboxes calling homosexuality a “curse of death”, while posters on bus stops in Melbourne carried the slogan “stop the fags”.
The material was “clear evidence that we’re in for a whole range of bile and offensive material,” Labor’s shadow Attorney-General Mark Dreyfus told ABC Radio on Tuesday.
Because the postal survey is not considered to be a formal election, it is not covered by normal campaign rules contained in the Electoral Act.
This means the advertising does not need to include a source. The Chinese/English letters did not have an attribution, while the Melbourne posters contained a link to a Neo-Nazi website.
Prime Minister Malcolm Turnbull was asked whether new rules were needed to regulate the campaign during a radio interview with Sydney commercial station 2Day FM.
“The only way to stop people saying things that you find hurtful is to shut down free speech,” Mr Turnbull said.
“In any democratic debate, [people will] often say things that are hurtful and unfair and sometimes cruel. But that is part of a debate.”
Labor senator Jenny McAllister, who is chairing a Senate inquiry into the postal survey, is encouraging those who spot hurtful material to alert the Finance and Public Administration Committee.
“We are already seeing examples of campaign material that doesn’t meet the standard of respectful debate. It is important that the parliament gains a comprehensive overview of the conduct of the campaign,” Senator McAllister said.
The Coalition has previously suggested it was open to the idea of special campaign rules for the postal survey.
“If there is a view that it would be desirable to have the usual protections that are enshrined in the Electoral Act available in this exercise then the government is open to work constructively and in good faith with all parties in the parliament to make that happen,” Senator Mathias Cormann told Sky News earlier this month.
Mr Dreyfus said there were existing laws that prohibited sending offensive material through the post, but they were weak and difficult to enforce.
“It’s going to need its own special rules which presently don’t exist,” Mr Dreyfus said.
