Well, let's look at it all from Clytemnestra's point of view -- from a mother's point of view (as well as from the point of view of any rational-thinking human being).
Your husband is hell-bent on making war, but his fun is spoilt when he can't get his darn ships out of the harbor. So he gets the brilliant idea of offering up your daughter -- your dear child -- to the gods as human sacrifice. How would you feel? Personally, I'd kill the bastard in a heartbeat.