Why did Australia's megafauna go extinct?

There are many different theories which speculate why they went extinct some of them are that an ice age occurred which wiped them out. Others suggest that due to climate change such as drying of the continent they starved to death. However, the one which is most accepted is that the Aborigines wiped them out for food. This is very plausible as they arrived roughly about the same time as the megafauna went extinct. Also the Aborigines practiced fire hunting which may have even further led to their decline and extinction.

This is ironic because the Aborigines invaded and wiped out the native animals land and stole it from them. Then the first settlers came and did to them what they did to the animals. But at least we didn't wipe them out completely like they did to the megafauna. Hell, all humans are animals in the end so why is it what we did to them any different what they did?

answ2. Megafauna are characteristic of an isolated landmass. The arrival of a competitor hastens the demise of these species.