Dont worry we have our killers too, snakes, spiders, sharks, crocodiles.
And although a Kangaroo and a Koala look all fluffy and cuddly i wouldnt want to corner one either, they may not kill you but both can seriously mess you up.
My dogs consantly chasing Kangaroos, once she had one cornered in a school playground and it wasnt happy. Those things can get very big.
In fact just the other week me and a couple other people were out the front of my house when a car slowed and warned us a kangaroo was on the loose, i quickly locked my dogs inside, seconds later this kangaroo comes hopping (i say hopping but this thing was freaking moving) down the street and in and out of yards. Poor thing was in a lot of distress, and it was a very big one. Very powerful tails and extremely sharp claws and they aint afraid to use them... i recall as a kid hearing stories of kangaroos kicking people and disembowelling them.... probably not true, but when you are near a wild one it make you think, when you see how far they can jump, and how powerful those legs must be, and how sharp those claws are. They are able to almost balance on their tales and front kick you..... not as scary as a bear or cougar, but still scary