Here are some of the common myths, with the truths explained:

Excuse: It is more natural to leave my pet unaltered.
Fact: It would also be more natural to live in a cave and not have pets at all. But humans have chosen to domesticate dogs and cats, and with that comes a responsibility to keep them safe, happy and healthy. See above for how spaying and neutering is an integral part of that responsibility.

Myth: My pet’s babies won’t contribute to pet overpopulation.
Fact: Even if your pet is a purebred, and you can find homes for all their babies, those are homes that could have adopted a pet – there are purebreds of almost every single breed  in shelters and rescues. And though you might be a lifetime pet owner, can you be sure that all your babies’ homes will never give up their pet to a shelter?

Myth: It will change my pet’s personality.
Fact: A dog’s personality is formed by genetics and environment, not by sex hormones. Ask anyone that has fixed their pet! There are some behaviors that are typically reduced by fixing your pet, but they are undesirable… unless you like a pet that territorially urinates, tries to fight more with other pets, or tries to escape to get out to find a mate!

Myth: My pet will get fat.
Fact: Just like with people, metabolism and food intake is what determines if a pet becomes overweight. Just visit a shelter to see all the overweight unfixed pets! Fixed pets can be calmer, so do sometimes need to eat less.

Excuse: My pet will never escape.
Sit at an animal shelter intake desk for 1 day, and listen to how many owner’s reclaiming their pets say exactly that. Accidents happen. Don’t let the accident be your pet escaping and causing yet one more oops litter.

Here are some more articles about the benefits of spaying and neutering your pet, and the myths and facts:

Myths and Facts About Spaying and Neutering
Spay/Neuter Your Pet