Define "life". Because last I heard, plants count as "alive" too?
One of the possible alternatives I'm aware of is ground up insects. Those are the same kind of "alive" as other animals, and yet AFAICT the "don't kill anything" people seem to things it's at least less bad. Even tho it takes a lot more of them to get the same amount of nutrition.
Are you aware of things called "obligate carnivores"? How do they fit in to your moral framework?
Have you played with evolutionary algorithms? Systems that have appropriate sensors / feedback loops to avoid harm to themselves (could even be as simple as a speed governor on an engine)? It can really be... odd to try to think of "life" (or even whatever term we're currently using to assign moral weight to anything capable of feeling pain) in general as being all that unique and special, when I can build something that meets most parts of most definitions in an afternoon.
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Humans are omnivores, and I have the teeth to prove it. Stop demanding that I forsake my heritage, especially over some half-baked philosophy that isn't even compatible with my experiences.