Originally Posted by TinkerTailor
"I won't kill you, but I don't have to save you... although... you know I could technically save you, but I don't want to... I want to kill you."
"But if I did save you, I realize that you will see this as weakness on my behalf and come back from prison because I left you alive."
Saving Ra's al Ghul would only make things go round and round and round as Ra's sees this as weakness in Bruce Wayne. Ra's is different than Joker in the fact that Ra's wants to die in a battle and not be left alive or he will keeping back back until he dies in battle whereas Joker knows he'll never die because even when he tries to corrupt any system he will be caught and locked up. That's why in Arkham City, Joker only dies because of his own machinations.