I think there is something missing from this discussion and that is the songbirds. Edwina is quite well-fed (!) and still her instincts make her go after birds. (If only I could convince her to go after mice, but that's another story.) Anyway, the only time she successful caught a bird she had absolutely no idea what to do with it. She certainly didn't need to eat it so it was simply needless killing of a bird. I have read that the song bird population is seriously depleted by house cats responding to instinct.
We don't allow her out without her halter -- which has a bell on it, her leash so we can stop her quickly and a chaperon! Consequently we have a great collection of birds at our feeder; cardinals, blue jays, robins, mourning doves, sparrows, woodpeckers, etc. for her to watch from INSIDE the house.