I know this post is late, but I was surprised by the controversy.
First, I would like to wish our Australian friends well on their national holiday.
I looked it up and found that the indigenous people are negative about it. In that way, it must be like our Thanksgiving holiday, and to a lesser extent, our Columbus Day.
One year my wife and I took the kids (18 and 20 year old "young men") to New England for Thanksgiving week. We spent Thanksgiving day in Plymouth and were treated to a steady dose of angry native Americans.
Usually our national holiday, which celebrates the Declaration of Independence, isn't controversial.
I noted with interest that Australian Day celebrates the arrival of a British Governor nearly concurrent with their loss of the American colonies.