They are not only useful, but protect against the whole bouquet of Western diseases. "China Study" to help you. Once the secretary general of China, dying of cancer, bequeathed to collect statistics across the country on nutrition, disease and life expectancy. Such statistics differ from generally accepted medical research in that they are not an intervention (when they intervene instead of A, they eat B, and they believe that B is useful, but in fact they are both harmful), and in that healthy people do not drop out of it (and doctors usually examine patients in hospitals). Colin Campbell collected the results from the United States, and the general conclusion was that diseases come in sets. To protect yourself from a suite of Western diseases, it is enough to follow the MDG - a whole, plant-based diet that is slightly stricter than veganism. The film "Forks instead of scalpels" and the book "Chinese research". The author as a whole encourages to pay attention to "research-emissions", which show the opposite of the paid result. Such results are rarely published, but this should not diminish their value. An example of an interesting research result from CI: complete control over tumor growth through the amount of protein. With a protein content of 20%, cancer wins, and with 5%, tumors do not grow, and in these experiments there was casein, and when replacing animal protein with plant protein, cancer does not develop even with a high proportion of protein. There are also statistics of popular causes of death. and an incendiary video on this topic from Michael Greger "Eradicating the leading causes of death" in favor of a vegan. It is difficult for a vegetarian to remain illiterate in the field of health and physiology, because too often they try to "save" him, and have to accumulate knowledge just in case. And knowledge already helps to be healthy. Personal experience: a family of 6, from 6 to 40 years old: 1 vegan, and 3 vegetarians, and two eat omnivores at school, at home for everyone there is almost always vegan food, rarely selectively vegetarian. We do not get sick with the exception of a couple of times a year in spring and autumn, recovering with sleep and lemon in 2 days. We all run through the woods, at any time of the year. We don't buy medicines. I never get a sore side when running. This means that prematurely leaking undigested food never poisons me. I don't think this is possible on an omnivorous diet. Before being vegan, I had an ulcer, then it disappeared. I can afford to violate many lifestyle and dietary guidelines while staying healthy by being vegan.
No, if you do everything according to your mind. But 90% of people do not do this in principle, which is why they look such goners. Also, if you are not one of the ideological people, and consider vegetarianism as a way of healing, then it is easier and safer to choose another diet - Mediterranean or its similarity - the diet of the Japanese from Okinawa. Their general meaning is quite simple - more vegetables and fruits, seafood, instead of red meat - fish and chicken. Nothing supernatural.
Regarding protein , plant foods also have enough of it. I will not go against the truth if I say that protein from buckwheat is as easily digestible as from fish or chicken. It's just that there is more of it in meat, but not to say that it is just horrible as much. In addition, meat is clearly more expensive and contains remnants of hormones and other nasty things that are fed to animals on farms.
A couple of examples
Buckwheat - 10-13 g of protein / 100 g
Carp (fish) - 16-17 g / 100 g
Chicken fillet - 21-23 g / 100 g
Beef - 18-23 g / 100 g
Lentils 24-25 g / 100 g
Peanuts - 24-25 g / 100 g
About Vitamin B12 - it can be taken in the form of pharmacy food supplements. You also tell that non-vegetarians do not drink pharmacy vitamins and minerals?))
Many vegetarians harm their health, because make up their diet incorrectly. Some lean on legumes, and they give a healthy load on the digestive tract, although they are rich in protein, others abuse dried fruits, which are high in carbohydrates, and they also get stuck in the teeth, which provoke dental diseases, others eat some salads, and walk in a fainting state ... This is only anti-advertising. I am not a vegetarian, but I was once, and I will say that this is a completely normal and working diet, if you understand what you are doing, but I would advise you not to complicate your life, but simply to cut down on unhealthy foods in your diet and more healthy, natural food.
Yes. Meat contains essential amino acids and rare vitamin B12.
But you cannot live on meat alone. Meat lacks the vegetable fiber required for pooping.