Overall, everything I say can be distilled very simply; you can take ANY fad diet - eating raw meat, eating only raw foods, eating only Soylent, eating only vegan, Paleo, Atkins and so on and so on, and you will find people who are SURE that all the research points their way. And those who follow the diet religiously (and it usually IS a religion in their lives) usually are healthier. Why? Because people eat less when they eat monotonous diets.
For decades we were told that "all studies show that eating fats are bad for you"
Guess what; what everyone knew was wrong.
There were far more studies saying that eating fat was bad for you than eating meat is bad for you, and they were all dead wrong. Switching away from fat led to a corresponding shift to carbohydrate and gave us the sick world we have to day.
People eat meat worldwide and life far healthier than many US vegetarians.
Why? Two main factors. (1) Amount of calories in US is excessive. A vegetarian fast food diet - fries (plant oil fried), Veggie Pizza, Veggie Chimichangas and all the rest - is a killing diet. (2) Excessive carbohydrates are a killer. Far worse than fat or protein.
For every study you show me on meat, I'll show you a study on how Tofu has harmful isoflavones. Or how beans contain lectins and have to be prepared very carefully. Or cyanides. Or green potatoes. Or you picked the wrong mushrooms.
Do more people die of steak or mushrooms worldwide?
The simple answer is to remember that fads come and fads go; and what we were told was healthy yesterday (margarine!) turns out to be a killer today (margarine - trans fats).
So just eat a balanced diet.
Furthermore, a balanced diet = a balanced ecosystem. Keeping chickens, ducks, etc. makes for a far healthier small farm than one based on sprays and poisons and artificial fertilizers. If we all subsisted on corn and soy, our farms would be soy and corn monocultures (bicultures?).
Our food should resemble a natural ecosystem - mostly perennials, mostly plants, some meat.
Anything else and you are speaking a religion, not a science.