If you choose to buy from a breeder, do your research to find a responsible breeder. Don't support puppy mills. Accidents can happen to even the most responsible pet owner. There are health benefits to spaying and neutering, and you won't produce more unwanted litters. This reduces the demand and market for puppies and kittens.
Older pets make great companions, and are usually housebroken and calmer than younger ones.
Sometimes financial and personal issues make it difficult to care for our pets. But they are our responsibility, and when we make the decision to acquire a pet we make a commitment for the life of the animal. Even if your pet is fortunate enough to find a new home, that's one less spot for another homeless animal, one more dead dog or cat.