It is a strange sort of conundrum, keeping and loving cats really. I love that my cats get to live as close to a natural cat life as it is possible for domestic animals to live that are confined at night for their saftey and receive regular meals and consider dogs (or at least my dog) to be their closest friend. And on the other hand you love other animals, and want them to also enjoy their lives and their endings.
When mine do have prey that I can not recover from them (and frequently I do manage to rescue what they have) I find it is a little comfort to remember that they are not torturing the animal they have caught, they are going through deeply ingrained natural responses to the presence of prey: tTeaching their young to hunt; honing their muscles and reflexes. So to them it is not an exercise in cruelty. That is a human interpretation of their behaviour, based on an assumption that cats think they same way we do. They don't and that is half their charm.
If you own a cat, you own a predator, and becoming accustomed to that fact can be a difficult process for many. I still have to leave the room if things get to the point where I can no longer usefully intervene on the behalf of the prey species.