This is some type of authoritarian argument. It's like saying murder isn't enough of a law.
Juries decide. It's based on the sense of the common man and what he would do. It's based on the sense of you wouldn't want somebody to do that to you.
I suggest you actually read legal history, instead of trying to justify from an arm chair the system we currently have. Our current legal system is radically different from the one that we had when this country was founded. And this isn't a philosophical discussion, it's actual history - and I'm on the side of the original one.
And for the support of this Declaration, with a firm reliance on the protection of Divine Providence, we mutually pledge to each other our lives, our fortunes and our sacred honor.