I don't know much about psychopathy, but is it generally accurate to say that psychopaths don't "understand" the ethical rules of society or the motivation for having said rules? I thought it was more that they didn't feel any sense of personal moral obligation to follow these rules or any sense of guilt when they don't follow them (while they still might completely understand the rules and their philosophical justifications, and may even be completely in favor of these rules existing and everyone else following them).

(Like I said though, I know very little about the disorder and am mostly conjecturing based on superficial familiarity)