Are animal byproducts in pet foods bad?
Although this analogy has its own issues, let's pretend your dog is a wolf in the wild. Your big tough wolf has just captured a rabbit for dinner. What parts of that rabbit is he going to eat? Just the muscle tissue? Not likely. He's going to devour almost the entire rabbit, including organs and intestine (aka. byproducts). In fact, these organs are where most of the body's valuable vitamins and minerals reside.
So what are animal byproducts? Basically they are what is left over after the intended product (human food) has been made and consist mostly of organs and intestines. This doesn’t mean byproducts are unsafe or lack nutrition — they just aren’t part of the original product for human consumption. For example, most people aren't into eating cow spleen or lung, but that doesn't mean your dog wouldn't love or get lots of nutrients from eating these organs. Some pet food companies have figured out the term byproduct has a bad rap and just list the organs added. Keep in mind they are still byproducts.
Byproducts can also be good for the environment. If we demand our pets eat the same cuts of meats as humans, we are competing for valuable resources and the environmental costs of animal production are high. If we want to help the planet, we should try and use all parts of production animals.
You wouldn't expect an animal in the wild to leave behind nutritionally valuable animal tissue, so why would you insist that your dog or cat food company do the same?