When faced with the choice of letting Ra's live or die, it really made me think of being in Batman's shoes. On one hand, you have Bruce living inside his philosophical-induced dedication to life and on the other hand, you have him beside his dedication to doing the right thing for everyone. This involves both the innocent and the guilty.
In the end, I chose to end Ra's' life and allow Batman to learn something from Joker's death in Arkham City: Despite the wish to see the deep good in evil and save that, redeem it, sometimes life is beyond preserving...
I let Batman do something very hurtful to his beliefs, his philosophy and his very being, to remind himself what the stakes are if he allowed Ra's to live - something worse than Arkham City and Protocol 10 next time? But it would've made him stronger and even more dedicated to life, more than what he would've thought.
And when Ra's said he was proud of Bruce for ending his life, I feel this was not just him being proud of Bruce finally knowing the stakes that Ra's always talked about, not even because at this point Ra's knew he had become the evil he fought against, but he said it to Bruce to reassure him that he was proud of the man and the hero he had become. Proud of Bruce putting himself in such a hard decision against his own philosophy. Proud of Bruce for showing the true dedication he has to all life.
That one word of Ra's' said to Bruce, it very much moved me.