Why don't all those who believe that Australia was invaded renounce their citizenship and attempt to return to wherever it was their ancestors came from?
Because in the majority of cases that option is not available. Any right to return to the original home of my forebears has long been extinguished by the number of generations to the present.
And many Australians were involuntarily dispatched from the Mother Country a couple of centuries ago with strict instructions never to return. If the descendants of these first white Australians were to return to the land of their forebears Australia would experience a massive shortage of politicians and other charlatans!!