Russ, have you actually read any of the links I've provided? I am a biologist, yes, which is why I can state with great conviction that cats are NOT a natural part of the ecosystem into which they are being released. They are also indiscriminate killers when they go out, they aren't just killing rats or starlings (an introduced "pest" species of bird), they kill whatever they can catch, even if it's an endangered species. Fledgling and ground nesting birds are especially susceptible. Keeping a cat in a house is hardly caging them (besides, no animal should be kept in a totally barren cage...even for pets typically kept in cages, you should build it in a way that it provides an enriched environment...tunnels, places to hide, plenty of toys appropriate for the pet, not just those that amuse the owner, and that allows all of the pet's normal behaviors to be expressed). Again, I've already provided several links that show how one should provide an appropriate indoor environment or outdoor enclosure for cats that meets all their behavioral needs. They have been domesticated; they are not wild, natural predators...they do not fend for themselves well without human intervention. Even the feral populations don't do all that well if they don't find a kind human to put food out for them.
I will not even bother repeating myself again about cats defecating. I'm not doing a size comparison here...a 7 lb chihauha digging up and defecating in gardens is no different than a 7 lb cat in size and destruction, except the cat is more certain to do the digging than the dog. Don't try making the argument about size, when that has nothing to do with.
Evo, before I started into this debate, honestly, I thought as you do, that as long as you live out someplace rural, where your neighbors are few and far between, and traffic really isn't an issue, you can let your cat out if that's what you choose...it's not infringing on your neighbor's property, and, like Russ, I thought, a "working cat" that is around for pest control rather than as a pet out on a farm, would be okay. But, as I've read more, it really seems they have the worst life of all cats. They get more parasites from the rodents they eat and fleas they pick up, on their forays, they encounter other wild animals, not just the little ones they're killing, and get into fights that leave them with serious wounds and infections, are left exposed to the elements and unhealthy/unsafe temperature extremes.
As for the feral cat population, it seems there's really quite a debate ongoing right now about how to deal with them. Generally, your approach is what has been common practice for some time...put out food, trap, neuter, and release. The debate arises for a couple of reasons. First, when you put out food, more cats are attracted to stay in an area, and that leads to growth of the population, more frequent conflicts between cats, and better success in reproducing for those you haven't caught to get neutered yet. The other, really big reason, is that nobody is collecting those cats on a regular basis to provide ongoing veterinary care, it's usually just a one-shot deal when you get them neutered. That leaves them not only susceptible to, but major carriers of, numerous diseases that affect both the feral population of cats and domestic cats they encounter. Cats left roaming in rural areas had a fairly high incidence of FIV. Rabies infections in roaming cats (feral or strays) are also a pretty high risk (again, nobody is getting them taken in for regular rabies shots). I even learned something new in the process...skunks can be asymptomatic carriers of rabies, unlike other animals that get sick and die fairly quickly after infection. It seems it's the skunk-cat interactions putting them most at risk for rabies. I know we do go to that effort with our farm cats here, of rounding them all up once a year to get them appropriate veterinary care, but the overall impression I get on non-research farms is that farm cats are not generally treated even that well (and once a year still means they aren't getting any preventative medicines for worms, and there certainly are worms for them to get out on a farm...those rodents they're supposed to be controlling are the primary vector for those worms, along with other diseases, which is of course why we're trying to control the rodent population...but, doesn't it seem even a bit troubling that we'll expect cats to come into contact with those vectors when we try so hard to keep them away from our livestock?)
This is the AVMA position statement on free-roaming abandoned, and feral cats:
http://www.avma.org/issues/policy/animal_welfare/feral_cats.asp
And, here is another site that discusses TNR programs from a bit of a pro and con perspective that gives some insight to why it's controversial.
http://www.holisticbirds.com/hbn03/spring03/pages/feralcats2.htm
And, Evo, really, why is it that you get upset if a dog escapes and digs up your garden, but don't think people should be upset when a neighbor's cat digs up their garden or scent marks all over it with urine? That's all I'm asking, is that cat owners give their neighbors the same consideration as dog owners are required by law to give. I'm also trying to take it a step further and help show the cat lovers here that "traditional" views of what is good for cats is inaccurate, and that the experts are recommending they be kept indoors or in outdoor enclosures in your yard, not just for good neighbor relations, but for the health and well-being of the cats.
) It also means they get exposed to other cats and feline diseases, pick up more parasites, chance getting run over by cars, and all sorts of other injuries. If you take the responsibility of adopting a pet, you should care for the pet and not leave it to fend for itself outdoors. And, if I saw a cat without a collar, I DID call to have them picked up as strays (we did have quite a few strays in addition to the pets...probably because the non-neutered pets were allowed to roam too).
And my mom also managed to back over of her cats. 
One day his dog killed two beautiful, sweet, kittens. That afternoon his dog mysteriously left town. It wasn't really his dog, I had found it half dead, and nursed it back to health and then he decided to adopt it, but he let him run loose all the time. A big hunting dog, purebred, I'm sure the new owners took better care of it.
...and they hadn't even left university property yet, but we weren't going to wait for them to do so). It is the owner's responsibility to keep the livestock on their own property. Had the cattle that escaped caused damage to the property here, the farmer would have been responsible for it. And, the reason I called the police the moment I saw the cattle rather than taking more time seeing if I could track down the farm owner/manager is that it could have been much worse had one of the cattle wandered down to the road. It's not a very busy road, but nonetheless, you don't want someone coming around a curve to find a cow in the middle of the road. 
But they are very cool. 
I am sitting in my chair STUNNED that you agree that confining an animal is good for its health...(And I don't want to hear your whole, "build it an ourdoor prison camp in your backyard" story again, that is NOT equivalent, and you know it) 
