I totally get that people might chose a vegan, or vegetarian, diet for themselves, I am almost vegetarian myself. What confuses me so much is when cat owners insist on feeding a vegan diet to their cats! An omnivore might be fine on a vegan diet, but a carnivore, not so much.
Cats need meat protein and they need taurine. It's not just that they like these things, or want them, they need them.
Go ahead and put some corn beside some raw (or cooked) chicken; even if you could explain to your cat the ethics of eating meat, and killing, the cat is still going to shrug its shoulders and devour the chicken. The cat is all about surviving.
There are actually companies that do manufacture vegan cat foods, but let us consider that the standards for pet food quality, particularly in the USA, are not terrifically high. Many lower quality cat foods do not have enough meat content in them, and cats are suffering health problems as a result.
Obesity is related to how much food a cat eats. Many low quality cat foods use an abundance of fat to add flavor to their foods that are lacking in a good meat source. Since these foods use fillers, and cheap protein, such as corn, the cat has to eat more food, all the time eating more fat. This is why so many cats experience problems with food vomit, their stomach simply cannot handle all the fat, or the other crap that goes into these foods, they want meat.
I am not going to sugar coat the cat food industry, baby male chicks are ground up at age day one to go into some cat foods (they, among other things, will be listed as by-products). If a person is concerned about such issues they can select a better cat food – one that uses only human grade meat, meat that comes from older birds. Heck an owner can cook for their cat if they wish, and can select free range, cruelty free, birds to cook for their kitty, or can pick another meat source (not fish).
Guess What? If your cat goes outside it will kill birds, it will kill mice. If you have a hamster and it gets out of the cage the cat might even kill that too. Punishing your cat for being a predator is totally unfair, and cruel.
Your cat is a carnivore, if you cannot deal with that perhaps a cat is not the right pet for you, perhaps you should get a rabbit. Stuffing your cat with vegetarian, or vegan, options is not good for it. Your cat is not a vegan, well, deal with it.