Some people say, hopefully with a good dose of irony, that murder is a victimless crime. In a twisted sense, this is almost true; once murder has been committed, the victim no longer exists (not as a person at least, though as a corpse), and as long as the victim still exists, no murder has taken place.
So why is it that we find the thought of murder abhorrent? Unlike rape or torture or even theft, in the case of murder, we're not around to suffer the consequences of the murder (assuming the murder wasn't preceded by other crimes), because we're just not around anymore. I think it was Mark Twain who said that, having not existed for millions of years prior to his birth, he surely wouldn't mind not existing after his death. So why is (unprovoked) murder one of the worst crimes there is, in almost all societies? Is it the fear of death? Is it because we don't want to witness others dying?