I got beat up on this topic once before on another blog, but just read another article so thought I would beat the drum some more. Not only are cats which are allowed to run loose more likely to be hit by a car, killed by a predator or be injured in other ways, they are the #1 threat to wild birds, and a significant hazard to other wildlife.
The American Bird Conservancy has launched a Cats Indoors campaign to make people aware of the threat cats pose to birds.
I understand the strong feelings people have on this issue. I am a cat owner and early in life allowed my cats freedom to go in and out. But no more. My 17-year-old cat has never been outside once we got her at the age of 6 weeks. Do your cats and the environment a favor and keep your pet cats in the house.