The chaos and uncertainty that has accompanied Parliament's dual citizenship crisis will be repeated in the years to come if the High Court accepts that ignorance is a valid defence.
That was the warning from former solicitor-general Justin Gleeson SC, who told day two of the court's "citizenship seven" hearings that Deputy Prime Minister Barnaby Joyce should be disqualified as an MP.
Appearing on behalf of Mr Joyce's political nemesis, Tony Windsor - the independent who ran against the Nationals leader for the NSW seat of New England at the 2016 election and is likely to do so again if the court orders a byelection - Mr Gleeson said section 44 of the constitution required strict "undivided loyalty" from MPs.
Dual citizenship did not need to be "voluntary, chosen or felt" to create a split allegiance, argued Mr Gleeson - who left his job as the government's top lawyer last year after a spectacular falling-out with Attorney-General George Brandis.
Clearing Mr Joyce and other MPs on the basis that they were ignorant of their status would set a dangerous precedent, he contended.
"If Mr Joyce's case is correct, the Parliament may consist of any number of dual citizens - it may be a very large number. If a person is diligent and inquires about their status and takes appropriate advice they will trip the wire of knowledge, they will be put on the horns of the dilemma," Mr Gleeson said.
"But a person is perfectly entitled not to seek advice. They are perfectly entitled to say 'I rest in my state of no knowledge about my foreign citizenship'."
This would create an environment in which political opponents, electors and the media would seek to catch MPs out and make them also "trip the wire" of knowledge: "We will then have a sequence like we have had this year of people in Parliament sitting there with this uncertainty hanging over their status."
There was nothing "exorbitant" about the New Zealand law that bestowed citizenship on Mr Joyce, he said, and there was a simple way for him to overcome this "disability" - by renouncing, Mr Gleeson said.
Senator Canavan's lawyer David Bennett QC also issued a grim warning, telling the court that every federal election would spark a "genealogical witch hunt" if it disqualified Australian-born MPs based on obscure foreign citizenship by descent.
Senator Canavan stepped down from cabinet after discovering his Italian dual national status in July. But Mr Bennett said there remains doubt as to whether Senator Canavan really is a dual citizen, with Italian constitutional lawyers still differing over whether a 1983 law change in their country automatically bestowed the status.
Mr Bennett argued Senator Canavan's status was so obscured by foreign law and family history it was not reasonable to expect that he would suspect he had any other citizenship.
The court also heard on Wednesday from Brian Walters, lawyer for former Greens senators Scott Ludlam and Larissa Waters - both of whom resigned when they found out about their dual citizenship status. Mr Ludlam was born in New Zealand and Ms Waters in Canada.
Mr Walters argued all five of the others before the court - Senator Canavan, Mr Joyce, Ms Nash, crossbencher Nick Xenophon, and One Nation's Malcolm Roberts - should all also be shown the door.
Section 44 aims to "reinforce confidence" in the Australian Parliament by ensuring it is occupied "by Australians and only by Australians," he said. The section ought not to be given a "tortured" meaning at odds with its literal, textual meaning.
The hearing continues today.
- This story first appeared on The Sydney Morning Herald.