Bob, roos can be a real pest, especially to graziers and farmers growing crops. Since white settlement in Australia roos have flourished due to land clearance, pasture improvement, improved water supply etc., and in places they can appear in almost plague proportions. Controlled shooting has taken place in some areas to prevent total destruction of the land, much to the horror of the animal liberationists, but it is necessary, and legal. There is no danger of them becoming a threatened species however, as they can be seen all over rural Australia in large numbers.
Koalas, on the other hand, are an inoffensive, peaceful animal much loved by all Australians, and tourists. Unfortunately, they are suffering the effects of habitat destruction as well as an insidious disease called chlamydia, which doesn't seem to affect animals which are not under any stress. However, animals who are suffering stress caused by the encroachment of humans on their habitat are susceptible.
Foxes, which were introduced to Australia by early settlers, are a real pest here too, as they are deadly on domestic chickens. I know, because we have lost numerous chickens to them over the years.
Peter.