I think it is more of a subject for psychology and evolution than theology. I don’t believe human beings are a product of design but a product of the self-organizing processes of learning and evolution.
I personally think that the psychopath is the product of a switch in human psychology which generally gets flipped when children are exposed to too much inhumanity and violence enabling them to turn into killing machines. It is largely a survival mechanism. But of course, all such evolved features don’t always work properly and sometimes the switch is thrown even when it isn’t appropriate and might even be voluntary in some cases. It also explains why this might happen more frequently in some races/ancestries than others.
Well I guess there is a theological question regarding the salvation of psychopaths. To that my answer is that only God can judge human beings properly. Even if that particular switch isn’t a choice in all cases, it doesn’t mean that they are devoid of any choices which matter when it comes to salvation.