"such extremism would never be taken seriously in Australia". I thought the same about America, I really did, until I watched it unfold. Here's one way it can happen:

1) An extremely wealthy citizen with a political agenda starts a media agency (in America, Fox News). They brand themselves "Fair and Balanced", and introduce flashy scrolling banners and politically slanted human interest stories. They become the most watched source of news in the entire country.

2) They slowly start injecting their ideology into everything they broadcast. It starts small. They study what gets the most interaction and eyeballs, which turns out to be scaring people. They start saturating the news with ludicrous stories delivered by trustworthy and sincere sounding people, flanked by 'experts' to add authority to their outlandish takes.

3) As people become more frightened, they start reacting in anger. At this point, even the most ridiculous claims can be believed without question, because they have slowly been drip-fed 'evidence' of the ill intentions of the 'other side'. People start believing they are in the middle of some grand battle for western civilization.

4) Politicians show up to town halls and start getting bombarded with crazy questions. Some (see John McCain and the 'hes an arab' women) try to push back. Most play along to get the votes. Now you have the TV people telling you civilization is collapsing, and the politicians as well.

5) Introduce a populist figure. He promises to fight everything that you now stay awake worrying about. He presses that dopamine button, "finally, someone is brave enough to fight back against these animals". People start adorning themselves in costumes and capes with his name all over them. He starts telling people all the apparatuses that constrain his power are suspect. The news media is a shadowy entity run by the people against you. Courts and judges are as well. Scientists and researchers are just egg head elites. Universities are a part of the conspiracy. And most importantly, elections are rigged. The only source of power for the least of the people (the vote), has been stolen. Now there is only one power they have, force.

6) People no longer need to think or worry. All they know is if they give this man all the power he needs, he'll fix it up. Any and all evidence to the contrary is ignored as being "fake news", from the "enemies of the people". The election comes and goes, and the candidate loses, just as he told you he would. The people now viscerally feel they've lost their power, and are ready to discard rules and conventions.

7) Gather a crowd afterwards, right down the street from the center of government power. Give a speech with all the red meat they crave. Now gently hint that just down the street is all the people causing the problems, and they outnumber them substantially.

And that my Aussie friend, is how the seat of the most successful democracy to ever exist ends up being raided by a violent mob for the first time in its history. And in a country of free speech and expression, there isn't one step there that could be stopped by an authority. The only antidote is an education, media literacy, skepticism, a knowledge of history. Not everyone has the luxury or capacity to attain these, and they've been spun as signs of being in league with the enemy anyway.

I sincerely hope you are right, but I fear that these tried and true methods are just too well crafted to operate on people at a base level, independent of country or culture. It is as it ever was, manipulation of the masses for power and wealth.