I think that he was right, but I also think that the duty is conditional. Duties in society are based upon a compact that contains a shared culture and values. When the culture degrades to the point where individuals (including those who hold (or did) an office charged with enforcing the laws of society) have a perception that there is a significant possibility that the victim will be penalized by the "justice system" (either by the process or the penalty), then there is no longer an incentive to the aforementioned duty.
When, after successfully defending against a criminal attack, society says that it will then place the victim in additional jeopardy, duty to said society evaporates.