Maybe you haven't heard about it but it is stated that Azshara had big influence on her people and almost all of them were blindly in love with here.They followed her because she maybe used some sort of magic to manipulate them.The closest IRL comparison would be Hitler and the German people that followed him,can you say all of them were like their leader,I don't think so.It was Azshara's idea to summon Sargeras and you can't condemn the entire race for following their manipulative leader.
Just think about it.