Perhaps you should refer to link below which gives a rather broader view of our involvement before, during and after the Vietnam war. It includes good and bad points from both sides of politics and the public.

wikipedia.org/wiki/Military_history_of_Australia_during_the_Vietnam_War

It'sdefinitely a fact that the returning soliders were treated shockingly by the usual anti-war groups and d---heads,but  I doubt if any PM or goverment could put a stop to it (that’s apparently democracy). But some of the “treatment” came from unexpected areas:

“In addition to the negative sentiments towards returned soldiers from some sections of the anti-war movement, some Second World War veterans also held negative views and attitudes toward the Vietnam War veterans. As a result many Australian Vietnam veterans were excluded from joining the Returned Servicemen's League (RSL) during the 1960s and 1970s on the grounds that the Vietnam War veterans did not fight a "real war". The response of the RSL varied across the country, and while some rejected Vietnam veterans, other branches, particularly those in rural areas, were said to be very supportive. Nevertheless, many Vietnam veterans were excluded from marching in ANZAC Day parades during the 1970s because some soldiers of earlier wars saw the Vietnam veterans as unworthy heirs to the ANZAC title and tradition, a view which hurt many Vietnam veterans and resulted in continued resentment towards the RSL.”