[nl]

There are multiple ways to attack this.

Firstly, understand the politics. The Labor party might tweak some corners on the legislation but will basically support it. Their policy is to support the government position on anything related to national security.

So any argument needs to be made understanding this.

At the moment the argument that "deliberate vulnerabilities makes us all vulnerable" has some traction, especially every time news comes out about a major hack. This is especially the case if it is linked to a state-actor, especially China or Russia. This is a good argument because it attacks the national-security justification.

Another good argument is one that was made to Turnbull on ABC Radio: Given your use of Wickr, what is to stop a foreign power from obtaining a warrant for an Australian politician or business person's communications? We already now of cases where the Australian security apparatus was used to benefit Australia's trade interest (in the Timor sea). Won't this make us more vulnerable?

Then there's the "Australia will be left behind" argument. If the US doesn't do this as well, then at least some US companies will refuse to comply and withdraw from Australia. That puts us at a competitive disadvantage, and if the same companies operate in the US it is hard to argue they are "bad".