The omnivore vs vegan argument as to who is right and who is wrong can be argued from a number of different platforms. There is the ethical issue of whether we should eat other animal life, and also the argument as which is 'better for you', based on arguments such as vitamin B12 is not available from a vegan diet. There is even the 'lifestyle' argument: does our lifestyle define our diet?
However, strictly, the only argument for or against either diet should only be made upon human biochemistry. Do both meet the needs of our biochemistry, or does one or the other lack something essential in our biochemical pathways? Obviously omnivores will lack nothing except by choice, since all foods are available for their consumption. If vegans do lack a specific chemical need, then is that available as a supplement in a form that can be effectively used in the chemistry of our bodies.
The one argument accepted by both sides is that it is essential for all animals to consume living things in order to stay alive themselves. These living thinks need not be alive at the time of consumption, but it is necessary that they eat the flesh of plant or animal life that at one time was alive and contained DNA. What that infers is that it is only vegetables that can survive on non-living tissue and this appears to be borne out in practice. No living animal known can live on inorganic matter only, but most plants can and do. Not all though, the Venus fly trap being an example.
It is easy to extend the moral problem of eating living tissue to living vegetable tissue that also contains DNA, and the argument must lie between animal and the derivatives of animals, and non-animal tissue. It has not yet been found that any organism has yet crossed the animal-vegetable divide, so the division is a valid one. That might seem obvious, but it is necessary to establish that for the argument between vegan and omnivore diets to be valid.
The consumption of protein derived from meat is not a prerequisite for size and muscle bulk, since the largest dinosaurs in the world were all herbivores, the largest being a member of the sauropod family at more than 175 tons, eclipsing the largest meat eater, the gigantosaurus at 8 tons. Thus, meat does not mean bulk. However, what has been proved is that the fastest creatures are carnivores. Hence if you want to be a top class sprinter, eat meat!
Carnivores, with their lean muscle mass and highly efficient quick use of available energy, have very short digestive tracts which are not good for digesting vegetable matter, but make best use of animal proteins and expel unnecessary mass from the body quicker. The argument in favor of the vegans is that the human digestive tract is not that of a carnivore.
In herbivores, the food takes longer to digest, and hence it remains in the digestive system longer. This means a longer alimentary canal, longer than humans have. Herbivores also move slowly, and a good example is the comparison of speed between the omnivorous chimpanzees and other small monkeys and the herbivorous gorillas and orangutans. On the one hand you have lean fast moving machines, while on the other you have large bellies and slow moving larger animals. Check out cows and sheep and compare their body fat with ours. Nor are we like herbivores.
So what are humans? Omnivores! Our teeth and intestines are those of omnivores, the teeth designed for ripping and tearing meat, and stripping leaves from trees, but also for grinding grains, and our intestines are something between the long and the short. People are able to eat and live on every type of food imaginable from brains to intestines to leaves to roots to ants and grubs.
The argument is therefore futile to consider historically. Let's then study the advantages and disadvantages of each type of diet. Human beings are capable of life through consuming either animals or plants, or both. The argument seems, therefore, to be one of morality rather than biochemistry. However, is that really so? The vegan refusal to eat dairy products should not be taken as extremism, since the human being is the only animal species to drink milk of another species, or to use it to make other products. It is a practice born long after cattle were husbanded by humans for food. The problem with eating animal products lies not in the meat itself, but in the fat. Animal fat is saturated, which means that the fat molecule has no active double bonds in the chemical structure that can be used to break the fat down.
Animal fat also contains cholesterol, yet we cannot survive without cholesterol. It is the human band aid, used by the body to patch up damage to the cardiovascular system. Only, sometimes, too much is laid down and the arteries get blocked. However, many vegetable products have more saturated fats and cholesterol than many animal products, so a balance is called for. The unsaturated fats and oils for humans are said to be derived from seeds, such as flax seed and fish, especially oily fish. These are the Omega-3 oils. Although they can be obtained from some seeds and nuts, it has been proved that the best come from oily fish, such as wild salmon, mackerel and sardines.
The B vitamins are essential for life. The best sources are animal sources, though you get them from some vegetable sources such as brewers years (who eats lost of that?) and others, but animal sources are the best.
Also, there is no evidence to suggest that vegans live longer than omnivores. In fact all of the evidence indicates that a middle road is the best. For human beings the healthiest diet includes both meat and vegetable tissue. The best solution to good health is neither vegan nor carnivore. Nor is it traditional vegetarian, since it is the dairy products that cause many of our dietary products.
Studies of the biochemical pathways have demonstrated that all chemicals need to sustain healthy human growth and life are not available from a classic vegan diet. Some animal protein and B vitamins are essential that cannot be obtained form a normal vegan diet. It is possible, however, to maintain life by means of supplements.
However, for the healthiest form of human life, our biochemistry, history and physiology indicate that there is a balance somewhere between the extremes of both views that is right for us, and that either diet can be sustained with appropriate supplementation based upon what is missing from one diet or the other.
So, omnivore vs vegan. Who is right: both are right if they also supplement any nutritional deficiencies in their diet with vitamins and minerals that may be lacking from one diet or the other.