I have always thought that extremists appear in Australian society when the balance is lost. With the increasing political closeness of the major parties, as can be well seen by the images above, I am not surprised at all to see the emergence of "extremists". They act to bring the system back to balance as the parties move in the direction of these extremists to limit their impact.
The major parties however are losing the faith of the populous which makes extremists more dangerous as if a major party falls too far a rapidly emerging extremist group could step into the void.
Just think it wasn't too long ago that many viewed the Greens as extremists.