I have a friend who goes out of his way to go further afield when looking for a new cat, mainly because the local population (largely un-neutered) is so inbred. He figures if no one else is going to neuter their cats then he might as well do what he can to diversify the local gene pool. There are so many scrawny inbred cats around here, that short of having someone organise a mass sterilisation program, this is probably the best thing (in his eyes anyway) that can be done to prevent the inbreeding.
As an example of what I mean, one of our neighbours probably is the nearest you can get to the Crazy Cat Lady fromm The Simpsons. One of her female cats has been pregnant at least once a year over the last 5 years. Typically they don't keep many of her male kittens, and the mother cat herself does not go out. So short of another male cat somehow breaking in and acting out a feline version of Romeo and Juliette, the only other way of her getting pregnant is by her own offspring.