Re: "but it's still an unnecessary waste of life"
"brains need meat to function correctly."
that's probably true, or at least ingesting cholesterol. [I have this theory about 'low cholesterol' meds and altzheimers...]. cholesterol is necessary for proper nerve/brain function.
In nature, carnivores and omnivores are the ones with the bigger brains, forward-facing eyes, etc. and with the exception of certain veggie-primates [who also eat insects, but that's easily/deliberately overlooked when pointing them out] it's the rule that if you have a big brain and forward-facing eyes, you're either an omnivore or a carnivore.