This type of diet can extend the lives of both cats and dogs and save millions of other animals each year. While both dogs and cats belong to the class carnivora, this doesn't mean a lot, so does the panda bear and they are near vegan. By nature cats and dogs wouldn't eat anything like what is commonly found in a can of pet food either. Vegetarian cats should be fed it as a supplement. Taurine deficiency can result in blindness and even death.
Cats also require pre-formed vitamin A and arachidonic acid.
All known vegan cat foods contain these essential ingredients. Ask your vet about changing your pet's diet if concerned. Not only is it possible to feed most cats and dogs a non-meat diet, it is also desirable. Also animals don't have morals or beliefs. They do whatever is necessary to survive, with no preference one way or the other about the impact on anything else.