I think a lot of the "multiculturalism has failed" folks wilfully forget that the main purpose of multiculturalism is economic growth, managing skills shortages and democratic stability but go off on the "brown people make us weak" stuff if it gets you clicks I guess.

We tried the "White Australia" thing last century and as a result while the rest of the multicultural world underwent a period of economic growth so large and sustained economists now call it "The Golden Age of Capitalism" our post-war slogan was "Populate or Perish" so .

But I guess if you completely ignored that the economic growth migrants, their children and their grandchildren have given Australia the economic strength needed to withstand multiple crises...

...and if you'd never visited regional Australia and seen how many migrant doctors, nurses and other healthcare professionals are helping to care for entire communities, or seen thousands of those same professionals on the front lines of the current pandemic...

...and if you'd never attended a university and observed how migrants provide billions of dollars of revenue to that industry while creating lifelong relationships with Australia that provide enormous future benefit in terms of soft power and direct trade...

...or if you'd never had any experience in literally any of the dozens of industries from mining and resources to manufacturing and export that benefit from the know-how of skilled migrants every single day with a net benefit to Australia in the billions of dollars per year...

...I guess I'm trying to say that IF you wilfully ignored literally every benefit of multiculturalism, while also viewing Australia through a prejudiced racial myopia (that had been rebuked by a court of law) then MAYBE you could make a case that "multiculturalism has failed".