His "Justice" was a war crime, an assassination attempt of a foreign head of state, cost the lives of uncounted Forsaken, Gilnean, Gnome, Dwarven, and Human soldiers, and the destruction of materials and equipment that were meant to be used to fight the Burning Legion.
Justice my ass. Dude had a vendetta, abused his position of power, and got a slap on the wrist for doing it. Anduin gave him a "Talking to"
Defection. Not "Leave if they want to". They were defecting to the Alliance in an apparent Coup attempt by Anduin to use Calia Menethil as a figurehead to start a Civil War in the Undercity to install a puppet he could manipulate (When Sylvanas made her decision). And then Calia threw off her hood and -actually- tried to sway the Desolate Council to follow -her-, instigating that coup. She even admits it at the end of Before the Storm and gets... gasp! A Talking-To from Anduin.
Did you read the book or are you just going off of people's arguments on the forums?
Parqual, the Felstones, and others were traitors betraying their people during a cease-fire. They knew the punishment for their crime was death because it has happened, before, that defectors tried to break their oath of service to Sylvanas and join the Alliance.
The SI;7 Agents bring Azerite to Shaw and Anduin before the Alliance Player gets to Silithus. Which means they got it from the Miners they were spying on. There's no crates of Azerite lying around for the spies to steal it out of. Wonder where they got it...
Nah, seriously, in the first chapter of Before the Storm, Anduin gets the rock from Shaw. Orders him to get all his best men on it. Basically it's the cutscene straight from Legion but longer. Sylvanas doesn't have her interaction with Gallywix until chapter 3. Everything in the rest of the book is presented as occurring in chronological order, including the jarring "Jump Cuts" during the Arathi Highlands sequence where the narrative's focus keeps changing from Anduin to Sylvanas to Calia. There's no reason to believe that the rest of the book isn't, also, in Chronological order.
Which means the Alliance started killing goblins before the Horde retaliated.