There were never any marsupials in NZ until the introduction of the possum.
But it's the same with the Mongoose introduced to Hawaii in 1883 to control rats and snakes or the cane toad into Australia in order to control the Cane and the Frenchi beetles. Back in those days there was not too much thought given to what could happen in the future.
We also have introduced the rabbit, goat, deer and wallaby which are in the wild, not in great numbers, but are controlled to a degree (well, not so much the rabbits)
Nobody has 'wild' animals (lion tiger, bear) as pets which could escape and we have NO snakes.