"Life is constantly fleeting from your grasp even from the very day it's bestowed upon you, but the shadow of death is always there, waiting for its chance to take you away."
"Even though many may not think so, ignorance and innocence are one and the same. The only difference is that one sounds nicer."
"I once knew a man who spent his entire life contemplating where we go after our death....it's a shame he realized it a second too late to tell anyone."
Money, nationalism, a way to kill without consequences, family tradition, a sense of honor or duty, etc....
I ended the list because that's all I could think of at the moment, but i'm sure there are others. The "killing without consequence" is the only bit i'd go for, though.
[Edited on 12.14.2012 6:53 PM PST]