It was not a unanimous decision to defend Theramore. You are making up a lot of fanon.
“You are a very persuasive woman, Lady,” said Rhonin. “While the Kirin Tor feels very strongly that we should remain impartial, your plea moved us to action. Even Aethas Sunreaver voted in favor of rendering aid. It seems that to not assist you against such tremendous opposition would be to tacitly support the Horde. At least, that’s the logic he used.”
--Tides of War
“It was my lord Aethas who cast the deciding vote.” --Songweaver, Tides of War
Aethas supported Jaina to become the new leader of the Kirin Tor.
“Not just on this. You’ve always been strong, my lady. In your power, and in your character,” said Aethas Sunreaver unexpectedly. “Even when tested and tried. And when you faced both an unimaginable horror and an inconceivable temptation—and were perhaps yourself tainted by the effects of the mana bomb—you still chose a path that was fair and just, rather than vengeful and dark. It is, you must admit, unlikely that anything else will ever tempt you so again. And I do not think there stands among us anyone who, were he or she in your place, could have done better. Indeed… we might not have done even half so well.”
--Tides of War
Aethas during 5.1 questline: "Silvermoon has been allies with Dalaran for over 2000 years. It is not a friendship we should toss idly aside at the whim of our "esteemed" Warchief Garrosh."
Under Sha influence, revealing his true feelings: "The sin'dorei must be free from the yoke of the Horde!"
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Because smuggling goods through a neutral port is totally the same as sending military aid...