If you extend that out to 15 years I'm also one of those "new passport holders" (though I do need to remember to actually push through my citizenship this year). My personal view is, there is a history to Australia. I want to learn about the history of the place that I now call home and the place that I love as my home, just as I researched the history of my homeland of the UK. Without reviewing history you will continue to make similar mistakes, its all part of growing as a nation.
We are Australians, our indigenous brothers and sisters (I'll use the non agro term) are also Australians, and ultimately my view is, there SHOULD be a day to celebrate Australian culutre, but it should also be a day that EVERY AUSTRALIAN can celebrate said culture. The fact that part of our community cannot celebrate Australia day due to the history that we should be learning from, is a problem in itself and enough reason to change the date to one that we all as Australians can celebrate the country and the culture that we love and enjoy.