1. It's not even Australian
It marks the claiming of the eastern half of the continent by the British. The name 'Australia' didn't even exist in 1788. Saying that Australia was 'established' is not only technically wrong, but offensive to the previous inhabitants, as department stores have discovered this year.
It's the founding of New South Wales, and because it's about NSW, it's not as national as you'd think.
2. It's a new thing
Only in 1994 did it become a national holiday. Seriously. It was only then that all states and territories made it a public holiday. There's no claim to a grand historical tradition of Australia day. The term 'Australia Day' has only been used since 1935. Before that, it was all about the Commonwealth and the British realm.
3. It's the day when a lie was told
It's the day when Australia was proclaimed to not have any humans (terra nullius). Up until 1967, Aboriginal and Torres Strait Islander people were considered animals; they were covered by the Flora and Fauna Act. In 1992, Australia declared it to be a lie that this land belonged to no one. Yay.
Aboriginal and Torres Strait Islander people choose to celebrate 26 January as Yabun. In the past it's been referred to as 'Invasion Day' but Yabun is flipping that on its head. It makes it a day of celebration of the enduring survival of Aboriginal and Torres Strait Islander culture.
So, we could change the day
I think Australia's the best country in the world, and I think there's statistical evidence for that in equality, wealth and innovation. We're the second most developed country in the world. Some of these maps show that.
But I think these things can stifle us by creating a 'halo effect' where we can't talk about our deep, deep, problems. Like that celebrating the day that laid the beginning of dispossession, war and genocide is not a good idea.
1 January 1901 was the day Australia came together and was created. The tea-totalling framers of our constitution clearly weren't hungover enough on New Year's Day and thought they'd whip themselves up a country. It's a beautiful thing that we weren't created through conflict and we could choose the first day of the year for our founding.
I can see how that makes it an awkward choice for our national day. Although it could be.
P.S. I'm aware that to most, 26 January is just another holiday for the beach, beer, boats and beats. One thing Australians can be relied on for is not taking national celebrations things seriously.