Thoth Mer
burning_eyes
If you are a cat owner you shouldn't let your cat go outside anyway.
They can be shot, hit by a car, or picked up by someone, and it doesn't have to be Halloween for cruel people. Coyotes will kill them, as can foxes and large birds of prey and flocks of ravens or crows, not to mention stray dogs and cats, and best of all, some dog or cat whose irresponsible owner thinks it's ok to let their dog roam around neighborhoods and alleys.
As well, cats have a huge damaging impact on the natural ecology. They kill birds and reptiles and other small animals. Parasites and diseases are most easily picked up from other outdoor animals as well.
I keep my cats indoors always and my dog is always with me. Where I live people would steal my dog if I left him unattended in the yard. There is plenty of stuff for them to do inside and there is no reason they need to go outside. Whether you choose to believe or not that your cat can be a hazard to the environment, or that there are very real dangers to your cat outside is up to you. It's your pet you say you love so much, and you're the one who will be missing them and worried when they disappear. You're the one who gets to pay the vet bills, and you're the one who will grieve when they are killed. But your pets are the ones who will truly suffer. Why would anyone want to risk the safety of their pet just because the pet wants to go outside?
burning_eyes
While in some places it is considered both foolish and dangerous to let your cat outside, there are a variety of places where indoor only pets are almost non-existant. The only wild animals around here are raccoons and hawks. Raccoons only come out at night and they can't get in my yard. And the only trees that a hawk could have lived in near me were recently taken down.
I worked at a vet office for a while as an assistant and the happiest and healthiest cats that came in were kept indoors at night, and allowed out in the yard during day hours.
A well trained animal won't attack birds, rats, or other creatures. My cats can sit outside on the porch within half a foot of the squirrel and be just fine. They also never leave the yard. There are many ways to train your pet to stay where it should and do as it should without shutting it inside. Unless you don't even have a fenced yard, in which case your best pet choice would be something in a cage or bowl.
As far as picking up parasites and diseases, they're actually almost always brought home by the owner. You go outside don't you? Of course you do. You have to pay the same vet bills as someone who owns an outdoor cat. All the vaccines and yearly shots that are given to outdoor animals, should be given to indoor animals as well. In fact, in my time with the vet industry, the only people who brought their pets in for diseases were owners of indoor pets who thought their pet didn't need any shots because it never went outside, unfortunately their owner harmlessly stepped in some dirt that a diseased animal must have either urinated in or rolled around in, because sure enough their dog got distemper, and because symptoms don't show right away, their brand new puppy got it too. It died. And their animal had never even been outside.
Also, if you live in an area would steal your dog if it was left outside, then I hate to break it too you but if it's that bad, your dog is no safer inside. I have a friend who lives downtown and someone broke into her house to steal things and then put her cat in the oven for good measure.
Oh, and this was mainly about cats. Dogs in general shouldn't be left unattended anywhere. When I had to take care of a dog for a while, he was only allowed to play in the yard if I was on the porch watching him.