Former deputy prime minister and Labor leader Kim Beazley fears One Nation's positions on Islam and free-trade pose a threat to Australia's national security.
"I think there are positions they adopt which are extremely dangerous to the country's long-term position," he told reporters in Sydney on Monday.
Mr Beazley, a former ambassador to the United States, said massive economies like the US, Europe and China could consider withdrawal from global free-trade agreements but Australia relied on them to survive.
"You have to be a complete moron to make an argument that you want to extract your 24 million (people) from that situation," he said, making reference to One Nation's skepticism toward free-trade agreements.
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Former Prime Minister John Howard, speaking alongside Mr Beazley, was in emphatic agreement with his former rival that One Nation threatened Australia's critical free-trade relationships.
"The way to handle any political party is through the battle of ideas," he said.
"In my time One Nation got into trouble when it had to debate mainstream economic issues like tax policy."
He said opponents should attack One Nation on that front, rather than "blacken their supporters" as political fringe dwellers.
Mr Beazley said he was also concerned about One Nation and it's leader Pauline Hanson's attitude toward the Islamic community.
He said Australia was "blessed" to be close to Indonesia, the largest Muslim nation, because it was "the least susceptible" to the strains of Islam espoused by some anti-West jihadis.
"She feeds them, One Nation feeds them," he said.
"I'm not going to make arguments about tolerance and all the rest of it. Those are important arguments but these are national security interests."
Mr Howard acknowledged extremists exist on both sides but he felt the Greens were the real threat "because of their hostility to capitalism and the American alliance".
