It's a tricky one Scotty.
The Aboriginal population have every right to see it as a day of mourning such was the horrific treatment they suffered for many, many years. However Australians today should be able to celebrate the founding of their country without feeling guilty for something they had no part in and indeed agree was a dark time in the country's history.
You could make the same arguments in the USA, Canada, New Zealand and no doubt other places the British and other Empires colonised.
I'm sorry I don't have an answer however I do believe that a solution is needed so every single Aussie can come together and celebrate for one day a year the most blessed country on Earth.
You may see it as a can of worms, I don't. It's something that should be addressed so you can all move on in unity.