My cats both stay permanently indoors - it was a stipulation made by the breeders and, for various reasons, it was my intention anyway. I do wonder sometimes if I am being cruel, but I guess that what they don't know they don't miss. We did try taking them out on a harness but they absolutely hated it - both the harness and the outdoors. I have a reasonably sized house which they have the complete run of. We have various 'cat gyms' for them to climb and jump on, loads of toys to keep them amused and we play with them lots. They are extremely socialable and loving cats as a result, unlike others I've had which only appeared when they wanted food or heat. We don't have to worry about fleas, worms, car accidents, bullying cats, dogs, dead birds, getting lost, cat-hating neighbours or cruel kids. It works for us, but it is a personal choice. I do think it would be cruel, however, to force a cat that has been used to going out to stay indoors.