From what I understand, animals aren't able to assimilate the nutrients when they are artificial/chemically made.

Some animals aren't built to eat such a narrow food base.

It's not as simplistic as source, but balance of ALL of the nutritional components required to thrive. If the essential amino acid proportions (part of protein that we ultimately need) can be provided by other than a meat diet, then that should meet the cat's protein needs (assuming it's eaten, digested, etc...).

Meeting the protein needs meat free might miss other nutrients that are needed though, vitamins, minerals, specific fats etc... The balancing act can be very tricky - ask any vet or animal nutrition major.

If I needed to avoid animal protein in my pet, I would work with a professional (vet or nearby university) to make sure any resulting diet is not deficient in anything. Certain deficiencies can kill.Cat food producers used to not know that cats require taurine. A lot of lives likely got cut short (cardiac effects etc) due to that mistake.

As to blackballing the applicant to a FB group based on such a thing, seems like malarky to me, with what little I have heard about it.

Well, well, well how small minded was that. What is the use of having a group at all then if people cannot have different ideas about life and what and how to feed ones cat. Petty. I am sure that if pussy feels like a bit of meat, he/she will gets its own.

Quoted by Raven CT below. I do feel terribly for how animals suffer in the process of providing food for humans and that we seem to not value that at all - and we are so distanced from it.

The examples are legion for how animals suffer in the process of providing food for other animals. Do you feel terrible about them? The food chain is the nature of nature. It is the way life is.

You can't teach a lion to eat Tofu. It wouldn't eat it and it would only become sick. and here is from
Gooniesnvrdie replied Jan 28, 2019
In 1955, those were considered true statements.

Why would a cat NEED protein from MEATS? Why would humans NEED protein from meat? Please I want to know, why meat protein is preferred over plant protein. Let's hear it.

I am gobsmacked you even ask the question. Even a casual knowledge of mammalian nutritional physiology sheds complete light on this.

Why do you think all cats and other animals such as killer whales are obligate carnivorous predators. Why do you think there are 600 species of parasitic wasps. Do you think these animals chose to occupy their food chain niche? They eat what they eat because they must being programmed by nature. If they don't they die or become ill. For details, do some research. I'm not going to teach you.

Blocking someone from the group is the wrong way about it. I don't want to debate the ethics of feeding a carnivore like a cat on a vegan diet because I haven't studied the science behind how harmful it would be (although I can draw some conclusions). That said, if we assume that it is harmful, I would still hold that banning the vegan from the group is only going to give him/her a persecution complex, not help them come to a better understanding of how to do things. If you want people to change, let them into a group that can show them a better example. If you ban them, you limit their exposure to intelligent conversation on the subject.

I think it's unfair and dangerous to assume that all creatures must eat the way we do. Animals have evolved the way they did for a REASON -- it's all a part of the ecological balance of the planet. For a vegan to assume that their cat can't eat meat because they don't eat meat -- and though it's a domesticated animal, a cat is a cat -- to put these limits on it is just being cruel -- and that in itself just seems ironic for a vegan. I know someone who's vegan who has six cats, and she's intelligent enough to know that they need to eat certain things... All this being said, if there are alternatives out there, then by all means go that route. But it sounds to me like these things haven't been developed enough, and until there's proof that they are viable, owners shouldn't compromise their pets' health in order to be "ethical."