This is about ethical requirements/duties versus practical constraints of people who keep stray cats as pets. This question and its discussion may be extended to stray dogs kept as pets, but DEFINITELY NOT to exotic species or even pure-breed dogs, cats etc. which are physically unfit to live in the wild.
This question is to be understood and answered in the context of ones duties i.e. Kantian ethics.
EXPANDING THE QUESTION: A pet-owner who adopts and keeps stray cats in his house, lets them come and go from his house as they please. Some of his pets wander away forever, while new kittens take their place -- either being born in his house, or being found abandoned on the streets. He allows his cats to mate and breed (though not inbreed incestuously), and he does not neuter them.
Whenever the number of grownup cats exceeds what he can reasonably accommodate, then he releases some that seem able to take care of themselves (say one-year-old cats) in a decent place far from his house, so that they are not able to find their way back to his house, but can be reasonably expected to survive on their own wits.
He believes that as he takes in lost kittens when they are tiny and totally dependent on care for their survival, he is not remiss in releasing grown ones into the wild, when they can survive on their own.
Also, he feels that justified in allowing his grown cats to breed rather than restricting their breeding ability by neutering them, as he does not feel that he "owns" the cats enough to tamper with their bodies in any way.
His actions proceed from his sense of duty towards cats, and not towards humans (including animal control activists who feel that any stray cat should be trapped, neutered and released).
He reckons that some cats that he releases into the wild may fail to fend for themselves, and will eventually die. However, almost all kitten from any given brood born in the wild die within a year, he reasons; this is the natural order of things, because otherwise, it would lead to an unsustainable population explosion within a few years.
His main argument against neutering both male and female cats is that it would prevent them from having a "normal cat life", and turns them into placid cat-shaped shells of their natural selves. Neutering them makes them "pets" but not cats, whereas allowing them to stay uncut lets them be cats, even though they may not always remain his "pets", he argues.
How to assess his behavior from the viewpoint of his duty to the animals that trust him and depend on him?