There generally isn't anyone I feel enough emotion about to want to go through the effort of having to kill them. I mean, yes, also morals and things, I'm not comfortable with the idea of violence, but on a more basic level I'm too lazy. You've got to go through the physical effort of killing somebody, by whatever means, and then the physical and intellectual effort of covering it up, and there's just nobody I know who matters enough to me to be worth that?