I've tried kangaroo jerky, it was pretty good! They also sell kangaroo scrotum's fashioned into little bags in Australia! When I went there I got one for my buddy. He was big into D&D, so he used it to carry his dice.
Killing something and wasting it is in poor taste.
Yes, once the kangaroos are culled, we should eat their meat, because they are already dead. Culling the kangaroos and eating their meat is no different than allowing people to shoot and eat deer in the United States. If the animals are dead, it is more environmental to eat their meat, rather than have to dispose of them.
I personally do not condone kangaroo culling, but if a kangaroo was to be sacrificed already, why not take full responsibility and not waste any part of your kill. It would be bad sport to simply practice the culling of kangaroos, and to let any resource attainable go to waste is bad practice.