"The indoor vs outdoor thing with cats seems to be largely a cultral thing which crops up from time to time"

It is cultural, and it is a question of education. People do things by routine or tradition without questioning. In Europe, there seems to be little interest in the studies that have shown the dangers and harm that free-roaming cats face and can cause.

To say that it is a question of "instinct" or that they are natural born predators is simply bunk. So are human beings. Should it be suggested that people abandon their homes and roam the countryside in search of food?   It would sure appeal to our natural instincts, but it ignores evolution.

Cats have evolved, like it or not. Domestication has changed the animal.

I'm sorry that this thread drifted, I do realize that it was about cats and birds - but there are bigger issues that are being ignored.   It is great that people are worried about declining bird populations, but cats are threatened too.