Dogs can survive and thrive on a vegan diet, as long as it’s fairly carefully tailored; dogs are not obligate carnivores, and the essential amino acids that they can’t make themselves are available from non-animal sources.
Cats are obligate carnivores; the only natural source for at least one essential amino acid they need is meat. (I’m not sure which amino acid(s) it is, off the top of my head. Taurine? Lysine? Something else?) In theory you could heavily supplement a cat that was on a vegan diet and not kill it, but given that bioavailability of supplements isn’t the same as that of whole foods, I wouldn’t bet a life on it.
I agree with you. Unfortunately, the law does not. The law privileges religion as though it was inherent and immutable.