I'm not sure I understand your dilemma. In order for something to be mutually beneficial, both parties must benefit. They benefit by thriving as a species, expanding their niche, and surviving. We benefit through eating them. I justify this through the fact that cattle made this choice through centuries of evolutionary process. It's not really a self-defeating argument. It was a choice for survival. What purpose would cattle serve if we didn't eat them? What would be the point of our "agreement"? The animals we eat today are not, and never were on the verge of extinction, because of humans. However, they have non-domesticated counterparts, all of which are either completely extinct or on the verge of extinction.
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