Whether or not a cat can thrive on a vegan diet is irrelevant to me as I don’t own a cat nor do I advise people on how to feed their cats. However, I do have a bias (as we all do) that tells me there is likely more nuance (which you did allude to in your original reply) than the general absolutist sentiment against the idea.

That bias is informed by half-a-lifetime of experience maintaining a loosely plant-based diet myself and witnessing first-hand the fierce compulsion people have to push their uneducated opinions at the mere mention of a plant-based diet. In my experience, there are few other things that can so reliably stir people into a vitriolic frenzy than the suggestion of a plant-based diet.