[E]ven a man of noble and god-like character cannot exist for even a single day without depriving other forms of life their life. This is the sad reality of human beings. Even a very honest and pure person must snatch water away from the earth without paying for it, breathe the air from the sky without authorization, and steal energy from the sun without paying. Otherwise, he cannot maintain his existence even for an instant. This is the sad fate of man. . .
Consequently, even if man really loves peace, in order to attain this noble aim of peace, he must kill the cow, kill the pig, kill the chicken, kill the fish, and kill the vegetables. To put it paradoxically, man himself falls into the scene of the great destruction of life caused by the survival of the fittest. Therefore, one can say that because there is no peace, he desires peace. . . .[T]he reality is that human existence is definitely based on killing. There is absolutely no human life that does not include killing or death.
From chapter 2, Zen & Budo, by Omori Sogen Rotaishi