Let’s see if I understand, Dex. We start out with a statement by God that the plants of the world were made to be eaten by the animals. There is no specific prohibition against eating animals recorded, but no specific permission to eat them, either.
Man eventually gets kicked out of Eden. No record exists that Adam and Eve were given any greater leeway in how they lived regarding food. We speculate that, as there were herders of sheep, sheep were eaten, but we also speculate that sheep were simply sheared or sacrificed. So, in the post-Eden, pre-Flood era, we have no clear idea what the acceptable (meaning, God approved) standard was.
Mankind reacts to its freedom from Eden badly. Eventually, Mankind behaves so badly that God is tempted to give up the whole experiment. Instead, God has Noah and his family survive a flood that wipes out all of humanity as it exists at the time (does this mean that genetic anthropologists should be looking not for Eve, but for Noah and his wife?). When the Flood is over, God tells Noah that “Every creature that lives shall be yours to eat; as with the green grasses, I give you all these. You must not, however, eat flesh with its life-blood in it.”
Now, presumably God is making it clear to Noah that Mankind has to live a better type of life than it did before the Flood. Before the Flood, Man had no permission to eat animal flesh. Does this mean that God’s “permission” to eat animal flesh, given after the Flood, recognizes that Man needs flesh to live a better life?
The alternate idea would be that Man never was prohibited from eating flesh, even in Eden. In that case, God’s words to Noah don’t provide permission for a previously prevented practice. Instead, they merely confirm to Noah that, just because God had him save the animals doesn’t mean he can’t eat them; they and the “grasses” are given to mankind as food. Thus, a confirmation of things as they were.
Your glib statement at the beginning of the report that, “This is an easy one. Answer: Yes, your friend is correct – the Bible presupposes a pristine state of vegetarianism” I think should be modified. One interpretation of the statements is that vegetarianism was the permissible lifestyle; this interpretation apparently has considerable support at least currently from Judaism’s religious authorities; your report didn’t make it clear how ancient were the interpretations of the statements in the Pentateuch upon which you are commenting. But alternate interpretations would seem to be at least as potentially acceptable based on the text itself. And the interpretation advanced certainly raises some question as to which lifestyle God has given an imprimatur to.