1- My research indicates that the only nutrient that cats need that can not be found in plant foods is taurine, and I found a vegan cat food which has synthetic taurine added to it.
2- The argument that vegan food can never be as healthy for cats as non-vegan food doesn't really work for me because there are tons of people who feed their cats cheap, chemical laden, meat-based food that is made from everything that was too horrible to put in human food. I guarantee the food I give my cats is healthier than that shit.
3- Some pet food companies actually use the bodies of euthanized companion animals in their food. Fucking gross!
4- Even if it is true that meat-based food is inherently healthier for cats than even the high quality vegan food, which I doubt, I just don't think I have any right to say "Because I know this particular animal personally, I am going to sacrifice the lives of many other animals just so that he can (maybe) be a tiny bit healthier than he would be otherwise. It just doesn't seem right.
5- I don't know what other people's experiences have been with feeding cats vegan food, but Kaya seems significantly healthier to me than he was before I changed his diet. He used to throw up all the time back when he was eating regular cat food. He still throws up sometimes ( he is still a cat after all) but not nearly as often as he used to. And Impala has been on a vegan diet as long as I've had him and he has more energy than any other creature I've seen in my life.
This is what my boys eat. Though, they only like it with nutritional yeast on top. Picky bastards.