Comic: X/1999 (X/1999)

Why not kill people? Because there are those who will cry about them. This is the answer. This applies not only to people. You can't kill living beings. Because there are always those who will be sad. You're sad when someone dies? Even if it's a stranger? Even if it's not human? Even if you don't know where or when he died? When someone kill someone. You want to cry? Nobody dies unmourned. Someone will be sad, no matter familiar or unfamiliar. So nobody needs to kill anyone.