There was also significant political advantage to having the Horde on Dalaran's side against the Blue Dragons and the Lich King.
In the end, people are people. Some Blood Elves are obviously going to place their loyalty to the Horde above their loyalty to Dalaran. Some aren't.
Please report any Code of Conduct violations, including:
Threats of violence. We take these seriously and will alert the proper authorities.
Harassing or discriminatory language. This will not be tolerated.