Good point in how carnism is indeed a belief or ideology. Larken makes the same argument statists and collectivists have used to justify domination of human populations for thousands of years. Not to mention humans ate mostly plants if any meat for thousands of years before fire was cultivated.
I think the strongest and most moral argument against eating animal products though, at least one that covers people who don't value non-human animals, is health and vitality. Self-interest is evident in nature, and for human beings who want and must survive, eating meat is detrimental to this pursuit. Interestingly, health and ethics go hand in hand.
True. That's the approach Jains take. Ahimsa is actually about not injuring oneself. Jains believe that by harming others, you harm yourself. That being said, needless to say, you can't force someone to do things that are in their self-interest. The road to hell is paved with good intentions.