Because human physiology evolved in an environment in which critical nutrients were sourced predominantly (^exclusively
animal in list below) in the flesh of animals.
This list does not include nutrients/vitamins which often lead to deficiencies when sourced in plants, due to very low bioavailability or antinutrients which block the absorption of the nutrients.
So, why do we kill and eat other living beings? Because we evolved this way and it is part of our natural diet.
Vitamin A: widely available in plants not sure why this is listed.
B6: also widely available in plants
B12: Should be supplemented, most people get this from fortified foods.
B12 deficiency is common across both vegans and those who eat animals.
D3: main source is the sun. again, deficiency is common across both vegans and those who eat animals.
F: This is common outside of the animal kingdom
K2: Found in soy
Amino acids: also found in most non animal foods.
Creatine: For most people your body produces enough of this to function. This can be supplemented.
Carnitine: your body uses the amino acids lysine and methionine to create carnitine.
Taurine: not essential
Heme iron: not essential and actually may be detrimental
CoQ10: commonly found in vegan diets
CLA: True, not found outside animals. CLA is controversial as there isn’t clear evidence on wether it is good or bad. It is not essential however.
Cholesterol: Your body makes it.
The most common deficiency among vegans is B12 I believe.
There are millions of people thriving on a vegan diet. They consistently test with better biomarkers than non vegans.
Many of your favorite celebrities are vegan, many athletes as well.
The largest associations for both the U.S and E.U recognize vegan diets as safe and adequate for a healthy life.
Yes we evolved to be able to eat many things and thrive. That doesn’t mean we need to.
I lived the first 18 years of my life as a healthy child that ate no meat. I now eat meat. Why? It's tasty and everyone else does it. Should we stop mass murdering sentient beings? Probably[1]. Is hunting and killing on an individual basis okay? I think that should be left to every individual to decide for themselves. If you don't want to kill animals, then don't. But don't stop me, a fellow animal, from doing it.
Perhaps you did not eat meat, but you almost certainly ate animal products of some form (eggs, butter, milk, cheese, yogurt, human breast milk or formula when you were an infant, etc.) which is all the animal-based foods you need to obtain the animal nutrients your body needs.
All human diets come at the expense of other animals and creatures. This is a natural part of life and shall always be so. It is false to beleive that there is a choice to make between slaughtering animals for food and peaceful coexistence with nature/animals. That's not an objective accounting and not reality-based.
For plant-based agriculture, first you take a plot of land away from the wilderness and native animals. Then you clear the land, purging its native plants (which are inedible and toxic to humans) and ground-cover, insects and any pest animals (e.g., birds, woodchucks, racoon, fox, rabbits, mice, to name just a few). Then you plant monoculture agriculture crop, which over time depletes the natural soil, worms and microbes of natural nutrients and requires increasing amounts of chemical fertilizers and pesticides. Animal pests continue to be killed as the crops mature, and then also by harvesting machinery at the end of the season.
A dramatized question: Would you rather humanely shoot a single steer (or goat/sheep or similar ruminant) which you could then consume over the course of a year, assuming you make use of the entire animal? Or would you choose to avoid meat, but in the process of eating an all-plant-based diet kill dozens or more wild animals and countless smaller pests and insects while disrupting local flora/fauna/ecosystems and depleting the soil?
Vitamin A... is available in plant foods in the form of precursors, e.g., beta carotine and similar carotenoids. These must be converted by your body into retinol, the animal and bioavailable form of Vitamin A. It is not uncommon for some individuals to be poor converters.
B6... (pyridoxal, pyridoxamine) is found in plants, but many of these sources require conversion, particularly beans and seeds contain antinutrients which reduce or block its bioavailability. Bioavailable B6 is far more abundant in animal foods.
"B12: Should be supplemented, most people get this from fortified foods... deficiency is common across both vegans and those who eat animals."
Stating that B12 deficiency is common provides a weak justification of the diet, which at its core exhibits a more pronounced deficiency of B12 than the broad population. Supplementation has its own problems with absorption and is not part of a natural whole food diet. If your answer is to supplement the many gaps of a vegan diet with supplements, isn't that a strong indication you're on shaky nutritional ground?
"D3... deficiency is common across both vegans and those who eat animals."
D3 deficiency is especially pronounced in certain kinds of diets, including vegan and vegetarian diets. D3 plays an important role in bone/calcium formation. Studies of vegetarians have linked low bone mineral density to their diets. Have you met adult vegans with osteoperosis or broken bones? To combat this during low-light seasons or geographies, a very good vegan source of D3 is lichens, the moldy looking stuff which grows on boulders. Have you ever tasted lichens?
"F: This is common outside of the animal kingdom"
Outside the animal kingdom vitamin F (linoleic acid) is found primarily in seed and nut oils. Seed/nut oils are not naturally stable and are manufactured through industrial chemical processes. They are high in polyunsaturated fats which also degrade in an oxidative way at high heat. Enjoy these man-made oils at your own risk and avoid using them for frying, searing or sauteeing.
"K2: Found in soy"
No. Or maybe you're thinking of K1. In the plant world, K2 is found only in _fermented_ soy, which in Japan is a slimy delicacy called natto which smells like sweaty gym socks. When is the last time you ate natto?
Vegans have to be particularly careful about methionine and lysine. Creatine, carnatine and taurine are found in animal foods and although your liver can produce them, the muscle fibers of vegetarians and vegans have been found to have much lower levels compared to those on diets including animal foods. Similar for heme-iron-- vegetarians and vegans have higher rates of anemia.
"CoQ10: commonly found in vegan diets"
CoQ10 is available at low levels in plant foods, but along with antinutrients such as oxalates, lectins and goitrogens, or in the form of seed/nut oils which I have already commented on.
"CLA: True, not found outside animals. CLA is controversial as there isn’t clear evidence on wether it is good or bad..."
When following an exclusionary diet, you're agreeing to forgo any potential benefits of some food groups. I guess one can hope that the case is closed on CLA, a nutrient in animal foods which the human species has been consuming as part of a natural diet for many millenia.
"Cholesterol: Your body makes it."
Yes, although body does make cholesterol, approx 1%-3% of the population is not good at making cholesterol. For this segment, their cholesterol can get very low unless they obtain it from the diet-- if they don't it can lead to severe neurological problems. The human brain is 2% of bodyweight, yet it contains 25% of the body's cholesterol. Are you aware that studies show that vegetarian and vegans have much higher rates of mental health problems? Perhaps it's just a coincidence.
"There are millions of people thriving on a vegan diet."
Veganism is a belief system (one which is noble, I should add). The diet part is full of nutritional gaps which need man-made supplements and powders, so clearly there are more optimal diets from a nutritional standpoint.
Nearly everyone can handle an exclusionary diet for some period of time before deficiencies catch up, gut issues develop, or mental health starts to suffer. Note that there are far more ex-vegans in the world than vegans. Odds are also good that you will become an ex-vegan in the future. I think that any diet in which you must study and plan your meals to obtain sufficient nutrients raises a big warning flag.
"Yes we evolved to be able to eat many things and thrive. That doesn’t mean we need to."
You may disagree, but my experience is that humans should eat a species-appropriate diet with a braod range of nutrients and minerals. Our bodies evolved on a physiological level to obtain nutrients from nature in a form which includes animal sources. Everyone gets to decide what they want to put in their bodies, so I salut your noble cause, but while I believe you are better than a standard american diet of highly processed carbs, seed oils and sugars, I do not believe your nutrition is superior to a natural whole-foods diet which includes both plant and animal foods.
Plants and fungi are living beings. We eat them for complementary reasons - what nutrition we don't get from one, we get from the others. I suspect you wish to engage in a veganist conversation, but until the "rules" are considered and applied with equal determination for fungi life forms, I have no interest in the debate that is most likely to emerge from this composed type of questioning.
Verbal cherry picking is annoying to all except those in the echo chamber. Nobody has ever said they eat hamburgers only because carrots are so hard to come by. Scarcity is a clever ruse, but doesn't work here.
Fungi aren't animals. They also don't have a central nervous system and they don't feel pain.
also in most cases not killing the organism by eating a mushroom.
If you are sticking to the argument so cleanly, then perhaps you can stick to my answer, which is at the beginning and not the end of the response you are speaking of.
As I predicted, the purpose of this post was vegan debate, and my answer has been completely ignored.
You could argue that marijuana leads to a spike in people eating lots of corn (Doritos), legumes (Taco Bell) and tomato (pizza). Not such a bad world to consider.
A fungus is able to search through a maze and apparently remember the route. Is it sentient?
EDIT: Your concern as to whether I was snarky in my response glossed over the fact that there is an answer. Let's talk about that instead of proving my "snark" as the more important yet correct part.
Why are you trying to prove that fungi are sentient? You're just being disingenuous. The core issue is the fact that we kill and eat animals that feel pain and emotions (the "vegan debate", whatever), something that seems wrong at face value. How about addressing that instead of hiding behind annoying semantics? It's obviously what the OP meant.
Look at your sibling comment for an example of a comment made by someone who actually cares about discussion and not winning stupid word wars. You both said the same thing in essence, but they don't come off as a prick.
Examples of key animal-based nutrients: Vitamins: A, B6, B12^, D3^, F, K2^; Amino Acids: Creatine, Carnitine, Carnosine, Taurine; Heme Iron; CoQ10; CLA; Cholesterol
This list does not include nutrients/vitamins which often lead to deficiencies when sourced in plants, due to very low bioavailability or antinutrients which block the absorption of the nutrients.
So, why do we kill and eat other living beings? Because we evolved this way and it is part of our natural diet.