I agree with most of what you're saying here. But the question now is why the tree of the knowledge of good/evil was so dangerous for them. It obviously destroyed the cosmos, their bodies, their union with God, everything. Now the big question is why.
As far as why the tree of the knowledge of good/evil is placed in the garden, I think the answer is clear: God is required to present all truth to Adam/Eve. So the truth is that evil exists, even if it is outside of the nature of God. The tree of the knowledge of good/evil is that truth. So basically, God has to allow Adam/Eve the choice between serving him or not. The truth is, they can not serve him if they don't want to. They decide not to.
The possibility of evil-of anything outside God's will- comes from the gift of free will given to man and angels. Evil arises as the gift is abused, as God is disobeyed. It's to choose a lesser good over a greater one; evil has no existence on its own since God didn't created it-it's simply the negation or decreasing of some good-it's a reduction or
diminishing of the perfection of God's creation in some manner-caused by our
choice. IMO the reason the tree is so dangerous is because eating of it-disobedience-is the rejection of God's authority-and therefore the rejection of God
as god for man. From then on man had no god for all practical purposes, even though we can't even exist without Him. Faith is so important because it's the restoration, from man's side, of relationship/communion with God, from Whom all life flows, apart from Whom we can do nothing, including control our desires which can cause great harm to ourselves and neighbor. So eating of the tree was a great injustice, a disorder in God's universe, that,
itself, constituted the very separation from God that defines evil. Man is called to recognize God's superiority; he's obliged to consciously subjugate himself to it. We just need to learn
why we should do so-something Adam apparently didn't yet know. As we come to know God we come to trust in and love Him. As we come to love Him we want to obey, willingly, having come to recognize His goodness and the perfection of
His wisdom over that of ourselves. Our own wisdom comes in recognizing and acknowledging
His.