Well, I never said the Watsonian argument here was rational - most opinions of this stripe seldom are. On a political level it wouldn't behoove Blood Elves with an Alliance grudge to blame the Forsaken (or the former Lordaeronians for that matter) because they're currently allies with one another, as both Blood Elves and Forsaken are members of the Horde. So an element of displacement is required, and the Alliance is represented currently by their capitol of Stormwind.