Below (in blue italic) is a portion of a reply that I wrote to a friend who was inquiring about Biblical strictures on diet and the slaughter of animals. As I don't consider the Bible to be an authoritative reference on anything, including food, I simply wrote a precis that might give her an alternate perspective and encourage her to research how food is produced and distributed.
I also wanted her to consider that humans have long used food as metaphor. Different cultures throughout history have complicated the simple act of eating with religion and ritual. Some people consider that they are traveling the moral high road if they eschew beef or bugs, or meat from animals with cloven hooves, seafood without scales, alcohol (Can you imagine?), leavened bread or the fruit of the tree of knowledge. It's time for us to concentrate on how to best serve our bodies needs for nutrition and pleasure in an efficient and safe manner.
Everyone on Earth should have enough to eat. We should raise our crops in a way that won't poison the land and the water. We should avoid growing mass quantities of monocultured crops (tomatoes, corn, potatoes) that could be decimated (possibly extirpated!) by disease, insect activity or drought. We should raise and slaughter food animals humanely and cleanly.
These are big, ambitious goals that will require fundamental changes in farming and agriculture, and they won't be easy to implement. But the longer we wait, the more difficult it will become. We have to look to the future.
.......Biologically, humans evolved to be omnivorous. It's true that we eat far more animal protein than we need, (thus providing a good living for cardiologists) but our cells do require a full complement of essential amino acids in order for them function correctly. There's no culture I know of (not religion, mind you, but culture) that ever chose vegetarianism as their diet. In fact, vegans and vegetarians are able to sustain their dietary choices because of our modern, highly technological society. It's only in the last few hundred years that we've been able to enjoy such a vast variety of plant foods, particularly soy and other legumes which provide amino acids that other plant matter doesn't. (Where would vegetarians be without tofu?) Most vegans and vegetarians also have to take dietary supplements to remain healthy; to replace what they're not getting from animal proteins. This simply wasn't an option for people who lived in earlier times or who live today in poorer conditions than Western societies. To them, meat is precious; costly and difficult to obtain.
Of course, there are monks, yogis, ascetics and various religious sects throughout the world who sustain a largely vegetarian diet in fairly primitive conditions. They also sleep on bare pallets, kneel on stone floors to pray and wear hair shirts in order to chastise themselves. These are the articles of their faith. They suffer (from anemia, almost certainly) as a sacrifice to their God (or Gods).
Factory farming, a cruel practice, is slowly coming under scrutiny in developed countries. It is possible to raise animals for slaughter without causing them to live miserable lives or die in pain and terror. (Reference author Temple Grandin for specifics on humane abattoirs.) It will cost more. We'll have to pay it. And we'll have to get used to eating less meat and more vegetables. It's that simple. Too bad that 'simple' doesn't mean 'easy'.