However, ignore the edge cases and there isn't so much ambiguity. Take the average American sitting down to a meal--why does he choose to eat beef? Typically it is out of habit or to please the palate. In the typical case, this act is harmful to the health of this person. This act also ends the life of a sentient being whose brain is developed enough to experience pain, emotions, and even develop social relationships. I don't see much ethical gray area here: a desire to please the palate would be trumped by another sentient being's desire to continue living and live free of pain and suffering.
Also, I doubt you would consistently hold to this position: "realize the ambiguity, complexity and downright contradictions that are endemic to our existence" if you were on the receiving end of the pain and suffering. If someone kidnapped your daughter and prostituted her out, for example, I doubt that you would find comfort in the fact that life is "ambiguous and complex".