The UN's Universal Declaration of Human Rights (proclaimed in 1948) recognises the right to freedom of expression. This includes an entitlement to hold opinions without interference, and to express ideas through any media without fear of societal sanction, government retaliation, or censorship.
Australians seem to believe that such formal recognition is only necessary because these rights are often denied in undemocratic countries. While this country is at the better end of the spectrum, Australia is not without its own restrictions. Some limitations, like legal sanctions on defamation and bans on disclosure of official secrets are widely accepted as necessary. The problem is that restrictions on what we are allowed to say go far beyond such limitations, and matters have worsened over time.
A generation or two ago, taboos limiting freedom of expression were fewer and different. One issue was the prohibition (especially for the media) on using the so-called seven dirty words. Certain types of views were also strongly disapproved of. These prohibitions included criticising religion, blasphemy, disapproving of the monarchy, promoting immorality (as then perceived), and expressing "unpatriotic" views (especially ultra-left or opposing a war in which the Nation was involved).
Changes affecting freedom of expression in Australia over recent decades (in my opinion) have had three main features.
Historically, it was mainly social conservatives that sought to place bounds on what was acceptable. A lot of old-fashioned censorship (both official and informal) had been based on the idea that families should be shielded from unwholesome material. Up until about the 1960s, even the ALP was socially conservative, and (consistent with this) Australian Catholics (for example) were a key part of its heartland. Labor also supported the "White Australia" policy. Until the Hawke era it also supported the monarchy, and Rudd and Gillard (while in office) believed that marriage had to involve a man and a woman.
Nowadays, censorial behaviour is more associated with the so-called "liberal left", is very much "politically correct" in tone, and tends to admonish or discourage the expression, publication and support of politically incorrect views on a range of contentious topics. Political correctness on many issues extends from the Greens and ALP to as far right as the "small l" or wet faction of the Liberal Party. The extreme left of politics (especially in the past) was often even more censorial, sometimes seeking to deny free speech to fascists, who were often defined to include a wide range of those with opposing views.
The second major change is that many individual components of the media appear to have become more overtly ideological and politically partisan, with newspapers and other media nowadays more openly backing political parties or causes rather than simply reporting the news. One clear example is the difference in editorial positions between the Murdoch Press (including Sky/Fox TV), on the one hand, and Fairfax Media and the ABC on the other, concerning many politically charged issues (e.g. asylum seekers, climate change, left/right politics). Partisanship often also extends to major private "think-tanks", many of which are politically aligned.
Partisanship is effected through the nature of news stories presented, the political leanings of columnists/presenters, and the content of editorials, letters' columns, and investigative reporting. Pejorative and laudative journalism is also common, with public figures often labelled using judgemental terms. These include words such as "moderate", "progressive", and "highly respected" (indicating journalistic approval). On the other hand adjectives such as "hard-line", "arch-conservative", "ultra-right (or left)", not to mention "disgraced", are used to subtly (or otherwise) indicate disapproval. These days often only a sympathetic element of the media will air particular types of contentious views or positively portray controversial figures.
The third major change over recent decades is that a much expanded range of views are now effectively discouraged. This has often involved a reversal in the direction of censorship/ disapproval. In the past, for example, abortion and homosexuality were generally disapproved of by society, and immigrant groups and Indigenous people were encouraged to integrate. These days populist (and often official) attitudes on these topics have been largely reversed, and those who argue against "progressive" views risk being labelled misogynist, homophobic, or racist. Over the same period coarse language, nudity and explicit sex in the media became much more widely tolerated
Political correctness(PC) is the overwhelming consideration driving most censorship in modern day Australia. It refers to promoting language, policies, or measures that are intended not to offend or disadvantage parts of society, particularly "needy" minority groups. Political correctness also encourages "talking-up" the achievements of selected groups (and programmes affecting them), often to the point of censoring news of failures. This is mostly effected informally through moral suasion and social pressure. Editorial policy in some media also plays a part, as does Government through either media policy or legislation.
Political correctness is mostly based on good intentions. It can partly be seen as a tactful attempt to treat (often marginalised) minorities in a nice way. (Pauline Hanson's politically incorrect attacks on Asian immigration in the 1990s were justifiably criticised, both for being unduly alarmist, and for needlessly making Asian-born Australians feel unwelcome). On the other hand, political correctness becomes pernicious, when it is used as a means of shutting down one side of a legitimate debate. Political correctness can also be used to attempt to enshrine minority privilege (affording rights and privileges not given to the mainstream community) or to force a single "right" view on controversial subjects.
In legal terms, a lot of political correctness in Australia is backed by a set of Commonwealth and State anti-discrimination laws (at Commonwealth level covering race, sex, disability and age). The Australian Human Rights Commission (HRC) and equivalent state bureaucracies play a substantial role in reinforcing political correctness in respect of designated client groups.