If you have never held a perfectly healthy animal while someone puts a needle into its arm to end its life, you may not understand the importance of having your animals spayed/neutered. There are not enough homes for them all.
Homeless animals are found in every community in every state, according to the Humane Society of the United States. Animal shelters in our nation process an estimated 6-8 million homeless animals annually. Approximately 2.7 million of these animals are euthanized due to over population. Remember, this doesn't include the thousands of feral cats and wild dogs that don't make it to shelters, many of which live precarious short lives.
Not only is it wise to spay and neuter for overpopulation reasons, it is also healthier for your pet. Spaying and neutering prevent unwanted litters, help protect against some serious health problems, and may reduce many of the behavioral problems associated with the mating instinct.
Spaying a female dog or cat eliminates heat cycles and generally reduces the unwanted behaviors that may lead to owner frustration. Neutering male dogs and cats reduces the breeding instinct, making them less inclined to roam and more content to stay at home.
Spaying female dogs and cats can help protect them from some health issues later in life like uterine infections and breast cancer. Neutering your male pet can also lessen its risk of prostrate and testicular cancer.
Most pets have better behavior after being altered. It does not affect their ability to do anything, except make more possibly unwanted animals.
Thousands of unwanted kittens end up at shelters every year.