I note that the question was originally put to "all religions," which doesn't seem to include atheists, but if nobody minds, I'll answer. I justify eating meat by studying how humans evolved, human nutritional needs (which can be deduced by watching what happens when some of those needs are neglected), and studying our dentition (our teeth). Excessively clearly, humans have evolved to be omnivores, and thrive best when they eat from a variety of food groups.
As the saying goes (that I think is the best diet advice ever): "Eat food, not to much, mostly plants." (Notice, "mostly" plants, not "solely" plants.)