Not my theory, but one that would retroactively make the Horde “morally grey” like Blizz said they would be:
Azshara and N’zoth put Sylvanas in power through Vol’jin because they thought they could make her an ally, but Sylvanas is playing them. That is why she destroyed the fifth world tree. Five world trees, five old gods…each tree, once destroyed, allows the destruction of an old god.
The faction war caused by the destruction of the world tree was not her goal but an unintended consequence that she then turns around for her own personal gain. By imprisoning Baine, she forces Alliance and horde to join forces to free him, and then once again they join forces in Nazjatar.
Had she not baited and then imprisoned Baine, the joint effort to free him would not happen, and tensions would be too high for a combined effort against Azshara and N’zoth. N’zoth wants Sylvanas to have the dagger because he thinks she will use it to imprison the world soul, but she will actually imprison him.
TLDR: Sylvnas foresaw N’zoth/Azshara’s coming BFA plan, and all her actions are to make it blow up in their faces.
Firstly teldrassil was freed of all old god taint in cata and secondly if that was the case why hasnt she burned the tree in hyjal that is in her backyard?
While I don’t agree that much with the idea the trees are super linked to them, it could be that since Goat boi is already “dead” via Aman’thul, and he was the fifth, it might not be needed.
I mean, since the Horde PC had no idea any of this 35 dimensional chess was happening, we still look like stupid, evil stooges for going along with all her batshizz plans to begin with. I have accepted that there is no redeeming this narrative, no matter what. All I’m hoping for is that the next expac hits some kind of hard reset on the story so I can keep playing without the story reminding me that I’m complicit in a genocide just because I picked the wrong color during character creation.