Wildlife and outdoor cats don't mix
I believe all cats should permanently be kept inside. I am a licensed wildlife rehabilitator yet I have four cats that I share my life with at this time.
Cats are not part of the natural ecosystem and will help destroy the environment if not kept from doing so. Cats hunt just to hunt, not because they are hungry. They kill anything that they can get to and often play with it while doing so, thus torturing the animal in the process.
There are so many dangers to a cat that is allowed out. Traffic, other cats, dogs, coyotes, other larger wildlife, and humans that do not want your cat roaming in their yards often harm or kill these pets. My indoor cats are perfectly happy spending their time watching out the windows, sleeping or playing.
I personally get to see the devastation that cats can cause on wildlife. So often I get in squirrels (birds and other wildlife also is effected) that have been maimed by cats. These are the ones that survive the initial attack by the cat. The must have antibiotics ASAP or they develop devastating infections that cause their deaths quickly. Cats do not discriminate between what you want them to kill and what you do not.
The lifespan of an outdoor cat is far less than that of an indoor cat because of all these dangers. Why would anyone not want a beloved pet with them and to keep them alive as long as they can? It is the human that must make sure that their pet is safe and that their pet is not killing everything, including endangered animals. Also most areas now have cat leash laws which means that if you allow your cat to roam unsupervised you are breaking the law. Neighbors who do not want your cat in their yard may trap it and take it to a shelter where it will cost you a LOT of money to get it back.
Why not keep a cat inside with lots of attention and things to do so that everyone can be happy?
5 indoor/outdoor cats.
I think it mainly depends on where you live. It's probably not a smart idea to let your cats outside if you're in the middle of a big city. I don't think I need to elaborate on all the things that could go wrong there.
I am fortunate enough to live on some acreage in the middle of nowhere, so I don't worry too much about our cats being outside (you have to have cats out here anyway, or you'll have mice).
They're pretty good about staying close to the house and barn, and we have kitty doors all over so they have free access to the barn, shed, and both garages.
They do come in the house a lot, depending on the season. In the winter, they're hardly ever outside, and in the warmer months, they're outside almost all the time.
The only one that stays in most of the time is my 18 year old, but even she like to go out once in a while during the summer.