I've been eating a plant based diet for over 19 years. No animals were murdered in the writing of this post
I agree that eating unprocessed, organically or wild harvested dead animal flesh has played an integral role in human history. I also agree that being a vegetarian is no free pass to health. There isn't any meat in a lollipop but you can't live on them. At least, you should probably not try to. It doesn't sound like a good idea.
In the over 13 years I've been working in the natural foods industry, mainly as a supplements guy, I've heard a lot of bullshit about both meat-eating and vegetarianism (my favorite is the woman who insisted she was allergic to water. That was awesome.)
The only consistency I have noted is that eating unprocessed food is probably a good idea. Whole, fresh, ripe, raw and organic fruits and vegetables are probably healthy. Dead flesh (while I think it's gross) has been eaten for far too long (unprocessed) for it to be bad for human health, at least when eaten in moderation (around 2-4 ounces a day).
It isn't necessary or beneficial for everybody to make blanket statements about what an ideal diet looks like. Food science is primitive, at best. My justification for saying so is the prevalence of disease in most industrialized societies. Processing food sucks. Plain & simple.
Eat what you're going to eat. If you want to be healthy, it is probably a good idea to eat locally, seasonally, and as unprocessed as possible. Other than that, your guess is as good as mine.
In the words of Michael Pollan, "Eat food. Not too much. Mostly plants."
Have a great day, everybody. Smile. Remember to breathe.