Just a quick note.
In a self-sufficient world with no laws, to prevent the upcoming of vigilantes or self-apointed groups of 'polices', we need to have a no-punishment policy for possible crimes. We cannot have people taking matters in their own hands, as this could very rapidly turn ugly. Without a court deciding upon matters of guilt or responsibility - not to mention evidence for the crime itself and whomever did it - no individual should feel the need to act upon a crime, no matter how hideous, and no matter how personal in nature, except when the crime is in progress, of course.
Thus we need to take action in preventing crimes before they happen, and when they still do, just turn the other cheek...
Social check ups and a strong neighbourly feel (without it being nosy) is one way to go about this, especially regarding matters of e.g. domestic violence.