>How is this a problem with indoor/outdoor cats?
It's answered in the same post you just quoted. They hunt so many birds they are destructive to the environment and are driving some to extinction.
It's answered in the same post you just quoted. They hunt so many birds they are destructive to the environment and are driving some to extinction.
The massive numbers of them are the problem. The only other pet as common is a dog and they don't hunt birds just for the sake of hunting like many cats do.
The only part of the complaint specific to indoor/outdoor cats is that they hunt even though a human will feed them. That's a complaint about the cats' morality, not a complaint about their effects.
It also assumes without justification that humans don't feed their outdoor cats.
The problem is any cats that wander around killing multiple birds. So many people have cats that even a small percentage of them doing this is super destructive to the local birds.