It is incredibly risky and should not be attempted by anyone who...
Actually, it just should not be attempted by anyone, ever, until we develop the right nutritional mixes (which we definitely do not have right now, not in a satisfactorily safe way).
Too many stories of cats dying because of their neglectful owners attempting to feed them a kinder diet.
We are omnivores. We can choose to not eat meat. Cats are obligate carnivores, they do not have that privilege. Feed them what they need to eat. If you have an ethical gripe (and it is perfectly understandable that you would, the meat industry is awful, that's why we're all here, aren't we?) to the point that you can't bring yourself to feed your cats meat, you should not have cats.
If you have a pet, you should know how to take care of it and be able to do so, rather than try to misguidedly force your own morals from your own human perspective on it.