I have just done a huge report at uni on "The use of 1080 as a pest control for possums in New Zealand" and I agree with some comments, they are pests, they are destroying the forest, but at the same time they are animals, its not their fault that the settlers released them for meat and fur trading. But then there is the fact that New Zealand's only native mammal is a bat and that all other animals are considered pests and pretty much can be destroyed with probable cause.
NZ also has a HUGE feral cat problem. Absolutely massive, with cats roaming the forests and killing birds, the only difference between cats and possums though is that there are far more possums and possums also ravage the flora.
I don't agree with any animal being shot for being what it is, but I do understand where the conservationists are coming from.