Well at least Nero had a reason for being the way he was, not "I follow a philosophy of hatred, mwahaha". What's the point of the Sith anyway? And don't give me that "abolute poweeeeeer" crap.
Star Wars, unlike Trek, is a basic good versus evil story. The Sith are, quite simply, the untilmate personification of evil, one of the elements of which are cruelty and domination over others. I don't think Lucas, for all the chinese and japanese psuedo religious themes, really meant for it to be any more complex than that.