I think that on this question, why not kill other humans, there are two kinds of people, those who feel empathy, and those who don't. For those who feel empathy, we don't have any urge to kill others, so we don't need rules and laws and the threat of eternal damnation. For those who don't feel empathy, the threat of eternal damnation doesn't seem to do much good, they need the threat of jail and execution, and even that doesn't stop some of them.
What is more interesting are more minor offenses, such as adultery, which is, IMHO, a victimless crime. What keeps you from straying (I assume you don't)? You can have a moral system which doesn't involve fear of God or the hereafter, the Stoics did, for one. Even if you never got caught, even if your spouse never knew what you did, you would know, and you might feel ashamed of yourself for violating your own code of honor. |