This gets trotted right out every time someone mentions their cat being let outside, as if it were some sort of awful sin and thus makes the cat's owner totally wrong in any worry or complaint they have about their cat's safety outdoors. It's ridiculous, particularly when there's a very easy solution to cats hunting local birds: a collar with a little bell. It's nearly guaranteed to ruin their hunting.
That aside, you yourself, as a human, are an invasive species that kills tons of animals indirectly through your habits each year, should you thus be enclosed 24 hours a day? Cats killing off random birds. The ship of human intervention in the ecosystem has long since sailed, and blaming cat owners for a relatively tiny part of it is an absurdity in badly applied blame.
That aside, you yourself, as a human, are an invasive species that kills tons of animals indirectly through your habits each year, should you thus be enclosed 24 hours a day? Cats killing off random birds. The ship of human intervention in the ecosystem has long since sailed, and blaming cat owners for a relatively tiny part of it is an absurdity in badly applied blame.