It's not built on "multiculturalism". It's built on English culture from English immigrants and their descendants.
"Immigrants" are not a coherent group. An anglo Birton and a dinka south sudanese in Australia are both "immigrants" - but their angloness and dinkaness respectively are vastly more salient facts about them than them both being "immigrants" is, as far as the impact they are likely to have on the country.
Do you imagine that everyone but white people are living exclusively in their original, ancient homeland? You cry about Israel, but the implication is that arabs are native to the area when its obviously not true.
Oh, and when jews started immigrating to palestine before the modern israeli state was created, the arabs furiously opposed this, often violently. Well, if opposing immigrants is such a terrible thing, perhaps the palestinians are paying the price for being xenophobic bigots?
SINCE, not until
And Australia has had a white majority for most of its history
What's this "we" crap? White Australians made it the country it is, which attracted other peoples.
And whenever those other people's weren't the product of highly selective immigration, they were very much not peaceful - see Lebanese, Vietnamese, Sudanese (and other africans) etc.
And if multiculturalism is so wonderful, why are you condemning colonisation? Australian wouldn't be multicultural without it.