I know that there are TONS of threads discussing this. But with new lore, i can make my case. And, if im wrong, please correct me.
Now we know what Sylvanas has been doin in Stormheim, she made a pact with Helya [ clearly evil ] to bind/control the Val'kyr queen, if im not wrong, to HELYA control her. Then Sylvanas would have an endless supply of val'kyr and be pratically imortal. So she wants to defeat a force of good, helping a force of evil, because she is more important than everyone else? Tell me when any in the Alliance did something like that man!