It's nice to have a conversation and/or respectful debate like this. All too often today, people get excessively rude or just shy away from discussing what their thoughts are all together.
I will definitely have a look :) As for your arguments:
1) A good example against this would be that our stomachs have more heme-iron receptors than they do non-heme; non-heme iron which comes from plants is not in a form that is usable by our bodies or is readily absorbed...and absorption is increased by vitamin C (we all know this) but also in the presence of meat.
2) The 'rotting' as you describe it of meat in our intestines, is actual a natural and beneficial process - bacteria in our intestines break-down and cleave proteins for us, so that we may absorb them...a symbiotic relationship we have with them, where we feed them and they help us with digestion.
3) I imagine our meat supply does not supply the B12 it once did or should; feeding animals antibiotics would effect their microbiomes and therefore, would effect the amount of B12 they could/should/ought to contain.
4) Browning/burning meat cause carcinogenic compounds to form. Some vegetables also form carcinogenic compounds when cooked and new research has indicated that the consumption of too much antioxidants actually increases the incidence of cancer, while under a certain threshold is beneficial. Antioxidants are present in plants sources; if we were to increase our consumption, to replace meat, then we would likely surpass this threshold.
One other point I'd like to add....if everyone became vegan, or got a lot more of their calories from plant sources....how much more land would need to be cleared and farmed to meet this demand? How much wildlife would be effected by this mass clearing and the side effects of commercial farming? Organisms living on a plant based diet, eat a lot more.
We do digest meat quite well - digestive enzymes called lipase and proteases. What we don't do well is digest the fibrous tissues of plants. Strict herbivores have to spend most of their waking hours eating and also have a digestive system (or process) that better enables them to digest and exact nutrients from this diet (ex. Rabbits eat some of their own droppings (2x digestion) and many others regurgitate their meals and have multiple stomachs (fermentation)). Our teeth would be considered those of an omnivore. As for B12, you're correct - there are other sources of it, but meat is the best source....most people don't like eating dirt and in the amounts required that would give them an equivalent dose of B12. I do agree that there are many problems with our food and how it's produced - meat, fruits, veggies, grains, etc....and that 'this' is the problem - not our diet.
All of which are likely correct. However, from a metabolic perspective, an increase in the consumption in meat enabled pre-human ancestors and humans to spend less time eating (because meat is more dense when it comes to calories) which freed up time to do all you described; provided the proteins necessary (or at the very least, a more abundant source) to grow a larger brain; and was a much better source of B-12, which the brain requires (as do all cells in the human body). As for a starch, yes this is a staple in our diets because it is broken down into glucose - which our brain uses as energy....but it is not 'built' from.
