How could anyone not become a vegetarian if he/she is bothered about killing other living beings?Fossil evidence suggests that among the reasons humans became, well, human, is that we began eating meat. Language might have been developed to help plan hunts (this is at odds with my own "instinct" of clamming up and pointing when I see a prey animal, which invariably results in everyone in the car looking at my finger instead of out the window at the beautiful 4' tall blue heron, but there you go). For thousands of years humans have domesticated animals for consumption of their meat, eggs, blood, skin, hair, fur and feathers. In the Garden of Eden, God gave all plants (save one) to Adam and Eve to eat; no mention of consuming animals occurs until much later. It is nearly impossible to eat a truly "vegan" diet: even plain rice has bug parts in it.
All of this avoids the question of whether eating meat is a crime, or part of the Natural Order.
Even if we got our big brains because we scored extra calories sucking marrow from dead animals, the past only creates the present; it does not define the present. We could give up our meat-eating ways. We could embrace them. To define our present, our selves, to make good choices about our present, we must be willing to confront hard choices and rise to the obligation and opportunity. Growth does not occur along the safe, easy path; the easy path leads to stagnation, unhealthy compromise, loss of autonomy, and a loss of connectedness.
Reading is hard; learning to read bothers children; should we let them skip over it? Marriage is hard; learning to be in a relationship bothers people; should we just toss out marriage? Raising children is hard; fighting the urge to send them back to God until they can be nicer is bothersome; should we just stop having children?
To avoid a difficult, potentially soul-rending task because you fear the outcome or have already made up your mind is unhealthy. Being filled with prejudgment is sick. To judge someone who has had the courage to risk growing is unkind.