It's amazing how many perfectly good animals get put to sleep every year because there just isn't enough room for them in the shelters. And thousands more kittens and puppies are being born every year, adding to this surplus and causing more animals to be euthanized. During kitten season, shelters are filled to overflowing with cage upon cage of kittens. The cages are so crowded that kittens have to sleep on top of each other. On websites, shelters plead for foster families to help them contain the overflow of kittens. But the kittens just keep coming.
Most shelters now will refuse to let you adopt their pets unless you solemnly promise to have them fixed when they are old enough. I went to MEOW (Mercer Island Eastside Orphans & Waifs) to get my two kittens, and since they were only 4 months old, they hadn't been spayed and neutered yet (veterinarians recommend that kittens be sterilized at about 5-6 months of age). In order to get my kittens, I had to sign a form that stated that I would spay and neuter them as soon as they were old enough.
When obtaining my kittens, I learned that they had been in their mother's eighth litter of more than eight kittens each, because her owners refused to spay her, saying they didn't want to deny her the experience of having kittens. Never have I heard a more preposterous reason. Cats do not have have sexual identities, they do not feel like "less of a male" if they get neutered, or less of a female if they do not "get the experience" of having kittens. Surprisingly enough, this is actually a relatively common concern among owners.
There are many organizations that will spay and neuter pets for extremely low prices ($18) in an attempt to encourage people to have it done. The SSPCA is even paying $20 for each pit bull that you bring in to get fixed!
There are also perks to getting your pets sterilized. In Seattle, it costs $33 to license an unspayed or neutered dog for 1 year, whereas it only costs $15 to license a spayed or neutered dog. For sterilized cats it only costs $10, whereas unsterilized cats cost $20. Plus, you get the peace of mind knowing that your female dogs and cats won't come home with puppies and kittens.