Why? Because I have friends who work in wildlife care and rescue, specifically with the group, W.I.R.E.S. They have up to date scientific information about the state of Australian wildlife. These people have informed me what the true state is with regards to kangaroos.
Secondly, think about it, how can a native animal be a pest? A cane toad, feral fox, cat, dog, buffalo, pig, ect. certainly are.