Yeah Australia missed that boat. We just wiped out a substantial proportion of the natives instead of importing slave labour en mass. Another topic methinks.
The definition of "lawful" regarding reasons to own a firearm or even multiple firearms is merely different here in Australia. Aside from the semi automatic class of weapons, and depending on the state laws, your collection ranb might actually be achievable in substantial measure. I don't know exactly what kind of firearms you collect of course, but some states collections is considered a lawful reason for owning a firearm.
Handguns not so much. They're fairly heavily restricted in Aus. Even long before port Arthur a close family friend had a 357 revolver of some description, and it was very carefully guarded as an illegally possessed weapon and never discussed outside that close group. Illegal weapons exist, but aren't often used in criminal activity, certainly not to the extend they seem to be in the US.
Self defence itself is not considered a legitimate use except in stringent circumstances such as police, bodyguards, armoured trucks etc. I saw a police detective recently and whilst he was essentially in plain clothes, the SA pistol at his hip was glaringly obvious and stark to my eyes as we just don't come across them in everyday life or expect to see them often up close.
It's culture. The overall opinion on firearm ownership here appears to be quite different to you guys.