if the animal has nutritious food and enjoys the food then the RSPCA would be fine.
the RSPCA published the following information:
it is possible to develop a plant-based diet for cats, these need to be carefully formulated to meet the unique nutritional requirements of the cat and be appropriately supplemented with essential nutrients
I hope the RSPCA, ASPCA, Whatever your countries local equivalent is looks into you with that sort of mindset
if the animal has nutritious food and enjoys the food then the RSPCA would be fine.
the RSPCA published the following information:
it is possible to develop a plant-based diet for cats, these need to be carefully formulated to meet the unique nutritional requirements of the cat and be appropriately supplemented with essential nutrients
Gish gallop
so the RSPCA would have zero issue with a cat on a vegan diet as long as the cat had adequate nutrition and was eating palatable food.
any argument with that?