Since I haven't and won't bother reading a book called Animal Liberation (The title itself is ridiculous), I don't know what the "naturalist fallacy" is, other than maybe the fact that it's "natural" for humans to eat meat appears to be fallacious for followers of Mr. Singer. If that's the case, I hardly see it as a trump card. Killing for food is not unethical. In fact, to the extent that meat has aided humans in evolving, it's very ethical. More meat, more evolution. And we certainly could use some more evolution.