First, we need to understand the distinction in question for ourselves. A conventional rule is one that is contingent, localised, and oftentimes produced by an authority figure (or figures) within a certain practical or social context. For example, I could, as a lecturer in a university classroom, create a conventional rule stating that it is impermissible to use a laptop in my class. Students would go along with this rule (I hope) because I have some authority in that context. Now, to be sure, I could have some good reasons for introducing that rule (laptops are distracting and they undermine concentration and deep learning), but I could also suspend that rule (maybe for a particular classroom exercise) and no one would say it was wrong for me to do so. The rule is purely conventional. Moral rules are different. They are not simply contingent or localised, nor are they capable of being suspended by appropriate authority figures. Imagine if I, as a lecturer in a university classroom, told my students that it was okay for them to torture one another for the purposes of a classroom exercise. They would balk at the notion. The rule against torture is not merely conventional. It is moral.

This statement is precisely the difference between what conventional rules are and what a moral compass should guide towards. As for accountability, there is a number of hard questions that need to be asked. Should violent psychopaths be locked up? Of course, for the exact same reason we don't let tigers roam our neighborhoods. Should they be killed? (see arguments on capital punishment). We are fascinated with the concept of psychopathy because it is rare and difficult to understand, we simply can't put ourselves in their shoes, we cannot fake not having empathy it's impossible.