I would assume that cats may have had a hand in the extinction of some species over the last 2500 years when they have been here. Just like humans had a hand in the extinction of wolves and bears from our island. Its not that I disagree that cats have a negative impact on local bird life its that the sparrow was a poor example. I am of the opinion that people should allow their cat outside or not keep a cat.

A two year old child is hardly comparable to a "prolific hunter" that can fend for itself in many situations (I mean in the UK here as our discussion has moved from why it is commonplace for the US to keep cats indoors to whether or not it is immoral to keep a cat indoors).

In terms of lifespan, yes indoor only cats do tend to live a little longer. However outside of the US such as in the UK, outdoor cats live the same kength lives as their indoor counterparts. For example I have owned 3 cats who have lived to 16, 17 and my current kitty is alive and well at8. My parents had 2 who both lived past 15 and my grandmother had a cat reach almost 23.

Additionally your link seems to be comparing solely indoor cats to cats that live solely outdoors as strays which will of course impact their lifespan due to not being provided to their needs by a human.