From a moral perspective, I would have to say the attack is unjustified. (From what we currently know) The Alliance and Horde are not currently at war, per the Before the Storm Book. I understand capturing this new "resource" and protecting it for yourself.. so any conflict in Silithus is fine... but going to the Night Elf home land... where they have lived longer than the Horde has been on this world, .. and killing a civilian populace.. is not moral or justified in game.