I don't think this hits as hard as you want it to. "Natural" arguments are going to hit on their face because, well, animals eat other animals, and if you're only not drinking an animal's milk because it's not natural, then are you okay eating one? No, obviously not. I like the arguments from a corporate farming standpoint that treats animals unethically, because it is factually true and morally justifiable from most, if not all, viewpoints. You should incorporate that in more, it's hard to defend against, but don't use "it's natural" because that is not a good argument.