You're the one who decide to take an animal as a pet, knowing all the damage it can do to the environment. If you're fine with it then that's ok for you but you can't force your pet to be in prison because you don't want it to kill other species, if that's the case then you should not consider getting one in the first place.

Would you want to live in a cage your whole life? Then why do you want to do it to others? Never heard of the Golden Rule: "Don't do to others what you wouldn't want them to do to you"?

I understand your point of view, I share it, cats are deadly to many smaller species that's why if you're against that then you shouldn't get a cat at all.

PS: Australia's problem is about the Feral cats and they are making traps in the wild to poison their skin thanks to some box trap and AI.