The only connection modern Australia as a whole has to the British monarchy is the arrival of the First Fleet. Britain founded "Australia" as a place to send their excess convicts. Their respect for the country was minimal, most didn't know it existed. By no means did the British monarchy intend Australia to grow into the fantastic nation it has become, entirely absent of assistance from 'Mother England'.
Today, White Anglo-Saxon Protestants make up only 18% of all Australians, according to the 2006 census. While most would consider me a 'typical Australian' - fair skin, blonde hair - I have absolutely zero connection with England. My ancestors came to Australia as free settlers rom Ireland, while an enormous proportion of the initial convicts that helped establish the Australian identity were from Ireland, or other British colonies. Migration has from all corners of the globe, especially since 1960, has been a huige driver of Australia's population growth, and today we pride ourselves on being a multicultural nation. Why then should thew Union Jack, so remote from the modern Australian identity, fly on our flag?
I don't dislike the Queen, I'm sure she'd be fine for a chat over a cup of tea, nor do i dislike British people in general. But I, as do most others, identify myself as Australian not British. Not half-Australian, half-British, either. Not even a little bit British. Australia has moved on from British affairs driving Australian affairs. There is no logical reason to continue the system of constitutional monarchy, apart from the obvious "if it ain't broke, don't fix it" arguement, which is really just simple laziness.
Becoming a republic provides great opportunity for Australia. While most agree the current system of government works well, redefining the system provides the opportunity to clear out the kinks (e.g not actually choosing our PM and Head of State). No longer do we hold trade obligations to the Commonwealth, and we can properly develop a multicultural identity free of the Union Jack. And don't worry, we are still invited to murder the Commonwealth Games and Ashes.
Beyond simple nostalgia for a simpler time, led by single-minded Anglophiles like Gerard Henderson, John Howard and our good friend Felix, there is no good reason to keep the Queen as our Head of State. The vast majority of Australians have no direct connection with the Queen, and yet she (and soon Charles) stares up at us from the two-dollar coin.
It's time to get up and move out of home.