so why don't most people relish in a good slaughtering?
They do, that's why they become a butcher.
But in all seriousness, there's no such thing as right and wrong, we're just brought up around the idea, and the morals are implanted into our heads as we grow up. Everyone's different though, some people naturally like a bit of gore and slaughter, others are complete pacifists, while others don't mind slaughter but won't do it themselves.