Thanks for the response. I won't respond to every point because (1) that would be long and (2) I don't disagree with everything.
> Human evolution and mutation is slow. By looking at what our primary diet was up until recently, we can understand the macronutritional and micronutritional needs of our body and how a vegetarian/vegan diet may or may not influence that.
What was "our" primary diet though? Depending on where a group of humans lived, presumably the diet varied greatly. It seems to me that humans can successfully adapt to a wide variety of foods. I'm sure early humans ate meat, but vegetarianism and pescetarianism date back at least to antiquity. And just because a diet kept us alive doesn't mean it's "good" for us in the modern sense. Say, hypothetically, that a meat-heavy diet increases the risk of early death. That would be irrelevant in the context of natural selection if that age is much older than that of typical reproduction. Our "goals" are different now, too. Does a person sitting at a desk all day require the same nutritional profile as a hunter?
> The main thing currently under scrutiny is the bioavailability and toxins (for lack of better term) of plant-based foods compared to meat.
This is interesting to me and something I've been researching too. It does seem that a lot of the "toxins" can be mitigated by using very old cooking techniques: soaking beans/lentils, cooking vegetables (rather than eating raw), sprouting, fermenting. These techniques can weaken the plants' defense systems, so to speak.
> Avocados, coconuts, olives and nuts stand out here, being more fat heavy, but as most of the population does not have a history with these compared to animal products, it is difficult to say its all good. Beyond that, it is very difficult to get all your minerals and vitamins just on those alone, which isn't the case for meat and seafood, which results in either tapping into the remainder of the veggies and fruit, or tapping into animal products.
To be pedantic: meat doesn't really have a lot of vitamins, right? If you want a complete mix of vitamins and minerals, you would need to eat the kidney, liver, brain, heart, etc, which for whatever reason we don't really do anymore (in the US at least). For the average person (again in the US), this means you will need to step into non-meat sources for e.g. vitamin A or vitamin C. I only bring this up because the topic at hand is specifically about meat, not necessarily eschewing all animal products, so they are presumably allowed in this context.