Actually from what this video shows Aethas fears that the actions of those Sunreavers that are loyal to Garrosh may cause what Jaina did later with the Purge of the Horde from Dalaran. The thing I love in this expansion is that it shows gradually how Garrosh becomes desperate and soon both sides will join forces to stop him.
with the horde she means all, but it's just Garrosh, even the blood elves hate him!
god.. where is Thrall? He has to speak with Jaina
Thrall won't be able to help with Jaina.
(spoilers) At the end of tides of war, after Jaina has lost her mind due to the mana bomb effect on her, she uses the focusing iris to attempt to destroy orgrimmar, before Thrall stops her and the two fight. He isn't powerful enough to keep her held off, and it even reaches a point she is prepared to kill him.
After kalecgos arrives and is able to calm Jaina and stop her from destroying the city, Jaina tells Thrall there long friendship is over, how because of what Garrosh has done, she can't trust the orcs again, even him, and may take years, if at all, for them to reconcile.