Most "no kill" shelters do not accept every animal that comes through their doors. They take in only the most adoptable animals and turn the rest away. These are the animals that come to shelters like ours. We never turn an animal away because we know that if we do, that cat or dog is liable to end up dumped in a rural area where it will meet one of several fates, none of them pretty.
Many of our dogs and cats are brought in by people who find them in their yard one morning, doubtless left there because someone who no longer wanted his pet figured he would "give the animal a chance." A chance to starve to death, get smashed by a car on the highway, waste away from disease? We at the humane society believe that death by injection is a more humane alternative for unwanted dogs and cats.
Even if there were enough space at shelters to keep all the unwanted dogs and cats alive for their entire lives, is that a humane way to treat animals who are bred to be companions to humans? I have seen dogs and cats who've been in confinement so long that they pace back and forth, over and over, not even noticing the people standing in front of the kennel.
The key to solving the heart-breaking situation where we have to decide to euthanize animals on a daily basis lies not in trying to keep all these cats and dogs alive, no matter what the conditions. It lies in drastically reducing the pet population through spaying and neutering.