Free speech is an accepted given.
No it isn't. There isn't a shred of legislation, bill of rights or constitutional guarantee to free speech in Australia. Even if it were mentioned in an Act (as the Crimes Act 'rights' are) that Act could be rescinded by Parliament. If it were added to the Constitution it could only be taken out by referendum, but the Australian people voted against that in the 1988 referendum.
UN conventions are not legally binding and the worst thing the UN can do to a country that ignores them is throw them out of the UN.
Nor is posting on the internet speaking, it's legally publishing.
UTS: Internet and online services - Communications Law Centre Have a read.