If it weren't for plants you also wouldn't be here typing right now, this is a fact. You don't need to consume meat, all those nutrients you are talking about such as proteins, calcium, enzymes, vitamins such as B12, can all be found in meat substitutes
And ? I don't understand the whole point of you argument here, if it wasn't for meat you wouldn't be typing here this is a fact, meat kicked human evolution ( a scientific fact) and meat cannot be be easily substituted not by any mean.
These are much more easily available to produce and create than real meat. The nutrition you get from each would be roughly the same, though I would argue that the substitution meats would have more nutrients because they are plant based, as well as having less fat and zero cholesterol. Therefore making these foods the most easily obtained and digested package of proteins, essential acids and sources if iron and Vitamin B12 that you can find as it does not take months or years to make.
Humans don't need the balanced diet you are talking about to survive, as like you said, we can easily supplement ourselves. Plus we don't have such a high risk of diabetes, cancer, or heart disease from eating healthy and delicious tasting food.
How is anything is easier to produce that something that occurs naturally? You need several type of plants, that grows in different region around the world that doesn't grow in the same season, from all around the world to substitute meat, how is this easier than meat by any mean? meat is available everywhere, even in places where plants are not available or rarely available such as polar regions, not to mention that when you are trying to subsitute meat by eating other plants you are over consuming other components from those plants and that's can be very harmful to the body.
Fat and Cholesterol are important to the body it is vital! (too much of them might harmful but that's another story) and this is not even an argument, the same way if you over consume some plants you harm your body being in terms of sugar fat and other components.
Without a balanced diet you have a high risk of diabetes, cancer (for example being 100%vegetarian increases dramatically the risk for colorectal cancer) or heart disease, and not eating meat and trying to substitutes to them you are putting your self at risk (example for the same amount of vitamin A on meat, you need at least 6x time more vegetables that contain it)
