I don't believe that killing living things for food is wrong. Of course you could be using the generic "you," in which case your point is irrelevant to the conversation.
so the only conceivable answer is to reason in such a way that it comes out with the answer you want
I don't disagree. If you find flaws in the reasoning by all means point them out.
- draw your arbitrary cutoff between important-living-things and not-important-living-things somewhere above plants and bacteria while staying comfortably below humans.
My cutoff isn't arbitrary (again I presume you are addressing me), and this is a mistaken presumption. If you endeavor to minimize suffering among things in the world capable of suffering, eliminating animal suffering is a net plus.
If you want to argue that since all living things suffer and therefore all of our food sources suffer and therefore any attempt to delimit an ethical food source is arbitrary, good luck. I eagerly await your finding that vegetables feel pain.