The carnivore-vegetarian debate is one of the several themes of the larger problem we all face. How do we find peace of mind in a violent world?
It's impossible to completely eliminate violence from our lives. Even the smallest movement implies friction and overcoming inertia. Even the primitive hunter-gatherer commits violent acts such as killing, harvesting, slashing and burning, though he/she lives more harmoniously on the earth than any other type of person. So the question becomes, "How much violence is acceptable?"
Just for myself, I've decided that driving a car to a burger joint and having a hamburger, perfectly normal behaviors in a contemporary industrialized society, consists of two acts, both of which are unacceptably violent.
We all want to do things which will enhance our lives and make us feel better, physically, emotionally, and spiritually. Fine tuning the delicate instrument of the self requires in-depth perception of the consequences of every little thing we do, and the unexamined life is a heedlessly unconscious one. A fool might think he's having a good time, according to the Buddha, but when the consequences of his foolishness begin to pile up "how bitterly he suffers."
Consider cats (and some humans), who are unable to understand the disastrous consequences for themselves of uncontrolled breeding. Their increase in numbers quickly outstrips the capacity of their habitat to support their lives.
Consider the "advanced" human beings of the modern industrialized world, who are just now beginning to understand the many consequences of using widespread industrial techniques of production and modes of consumption, including consumption of factory-farmed animals.
I'm convinced that if we fully understood and acknowledged these consequences and the effect they have on our ecological, social, and individual existence, we'd all be vegetarian.
Life today in the kind of society we live in is extremely complicated and hard to understand. We're all mentally conditioned by the institutions of this society -- its governments and educational establishments and corporate enterprises -- to accept "the way things are." The nature of reality has always been elusive (see Lao Tszu); perceiving it while living in our present circumstances is harder than ever. Doing so requires overcoming the social conditioning we're all subjected to. But if we fail to understand it, we amplify our own suffering, as well as the suffering of other creatures, human and non.
Philip K. Dick, the science fiction writer and mad philosopher of California, once said that reality is that thing which, "when you stop believing in it, it doesn't go away."