You mentioned outdoor cats are bad for the environment and the cats health, however what if the cats nature/personality would mean it would be miserable living inside all the time?

vet-and-wild:

There are plenty of ways to provide stimulation for an indoor cat without letting them roam unsupervised! Providing window perches, different heights and types of cat trees, rotating toys, food puzzles, hiding spots, and interactive solo toys are all things you can do to keep your indoor kitty mentally and physically stimulated. Also, clicker training and interactive play with your cat are great ways to be directly involved in stimulating your kitty! Here’s a link to a great article about cat enrichment.

Clicker training with my cat, Garrus. And you can see his tunnel in the background, which I rotate with other toys and boxes.

Going outside can be used as enrichment too–but they should be under your supervision, not roaming free. Instead, leash training your cat or providing outdoor enclosures are much safer alternatives. Leash training my cat was the best decision I’ve made for him. He is able to enjoy the outdoors, but in a safe and controlled manner. Here’s a little more information about leash training a cat. Indoor cats can become overweight, stressed, and develop behavioral issues if we as owners don’t make an effort to provide enough enrichment and exercise for them. However, that is not a good enough reason to let a cat roam outside where their health is at risk and the environment is at risk. What I would say for a cat that is miserable inside is that they are not receiving enough mental stimulation, not that they are incapable of living happily indoors. I know it can be hard to keep up with them; my cat spent half the night biting my toes because yesterday I did not do enough to stimulate him so he was totally bored and full of energy. Just keep reminding yourself that keeping them inside is what is best for them and the environment!

Garrus enjoys playing in the grass while out on a walk. Leash training is a great alternative to letting a cat free roam.

Think about it this way.

Would you rather have a cat who’s safe but sometimes bored, or a cat who’ll probably die a violent death and will undoubtedly be responsible for the slow, excruciating deaths of several hundred small animals?