I think it's less applying their morals to the cat and more not wanting to support the meat industry. That said, yeah just don't have a cat. I expect many vegans aren't too big on the concept of pet ownership anyway.

Cats aren't just hunters. They're obligate carnivores. That means they literally can't get all the nutrients they need from a plant based diet. They need the vitamin A in meat in the same way that we need vitamin C.

I blocked all those vegan subs when this shit happened, they were already pretty bad tho.

Like if someone posted:

I'm not vegan but am looking to eat less meat

They were banned, so I figured out I was better off blocking than stumbling in one day.

But the original was just talking about feeding cats human vegan food. Then after admins stepped in, some mod went and found a single research article that said it could be possible with supplements...

But I think the supplements came from animals anyways?

So they advocated for something that would harm pets, then found the absolute bare minimum "proof" that in a very narrow situation no one was doing it might not harm the animal "significantly".

It legit seems like they're just trolling and trying to make vegans seem insufferable

It’s not. Cats have a super high protein requirement. So much that dogs and humans can die from kidney failure if they eat only cat food.

The idea of Obligate Carnivore is fully lost on some. And that’s quite a sad reality.

It seems to me that a lot of people are using that term without knowing what it means. That, too, is a sad reality. It means that cats in the wild aren't able to live off non-meat sources that they can find there, similar to how humans can't live in subfreezing temperatures without shelter or clothing. It says nothing about whether their dietary needs can be fulfilled without meat in a domestic environment. Maybe yes, maybe no, but you can't just parrot the words "obligate carnivore" like a Fox News anchor and act like that gives you the answer. The world is more complicated than that.

In fact, based on other info, cats do seem to be able to survive on human-supplied vegan diets, but it's less clear that they can enjoy optimal health on such a diet. So the reality seems to be somewhat shaded.

Even for humans, being a well-nourished vegan is somewhat difficult (you have to pay attention to stuff like protein combination). It's even harder to be a so-called "raw vegan" (living entirely from uncooked vegetables such as in salads) but apparently it can still be done. Most human vegans consume a lot of beans and grains that are inedible without cooking.

You can imagine an animal species for which cooked beans and grains would be a completely healthy diet, and yet that diet is never seen in the wild because wild animals don't cook. Thus they would get their protein instead from animal sources, i.e. be obligate carnivores, even though they would be fine on steamed rice and tofu. There is no logical incompatibility between "obligate carnivore" and "vegan diet". It's a question of biology that is species specific. In the limit, you could inagine a Star Trek replicator synthesizing perfect mouse meat from pure carbon and other elements, giving you a completely healthy and satisfied vegan cat that thinks it is eating freshly killed mice.

It doesn't appear possible for humans to stay healthy for long periods as fruitarians (some people don't want to cut or kill living plants for food, but instead live off of fruits and nuts that have naturally fallen off the plants). But that can only be known through experimental observation, not linguistic knee jerks. You have to examine the details to understand the real situation for any particular species, food type, and preparation method