I'm confused by the Ally's claim that Theramore was a peaceful city. It was strategic post that was very close to Org. If it had actually acted as a neutral city and removed itself from the war effort then I could see why they would be angry when it was bombed, but they used it as a launching point to attack the Horde on many occasions. Using this base, the Alliance was spreading into the Barrens and wiping out small Horde towns including a peaceful Tauren hunting town. Camp Tarajo was a slaughter of mostly civilians.
Why would the Horde not have a reason to wipe out Theramore? How many innocents should they let the human soldiers kill?