Frank Castle was a highly efficient soldier during his time in the army. In his various origins, he’s been everything from a gifted infantryman to an exceptionally deadly black ops soldier. In either case, he saw combat action, killed enemy combatants, and came home a war hero, ready to return to his family. When tragedy strikes again and his family is killed by criminals, Frank Castle enlists in a new kind of war, creating the Punisher persona and violently lashing out at criminals.
Over many years, the Punisher has amassed a frightening body-count. While colloquially, any civilian individual with a kill-count in the triple digits earns the title of a “psychopath” or “psycho” in the public consciousness, there is a lot more going on with Frank Castle's psychological pathology. The label of psychopathy falls apart quickly when examining the character deeper. Frank clearly has a love for his family, and feels their loss. However, one of the hallmarks of psychopathy is a lack of care or love for other human beings. Rather than being a psychopath, Frank Castle instead presents more characteristics corresponding to a sociopath, or a narcissist (and an extremely accomplished one, at that).
Classifying the Punisher as a narcissistic sociopath makes a lot more sense than calling him a psychopath. A narcissistic sociopath is someone who acts without concern or regard for the actions or emotions of others, and is drastically set in his ways. He rarely cares if a criminal expresses remorse or shame, and once Punisher gets his hands on them, they’re as good as dead. In that context, Punisher’s pathology manifests the loss of his family not as the loss of kin, but as the loss of possessions, or the extension of Frank’s will. In that context, Frank loves his family more like things that belonged to him, but now he can’t get back. Frank feels psychologically challenged by the criminals, and responds to that challenge with the means that he deems most effective: extreme violence and prejudice.
An ordinary man would likely eventually grow tired of his life of violence, and make peace with the fact that his family is gone forever, and no amount of blood will bring them back, or make a substantive difference. Frank, however, feels that since his “possessions” are gone, with no way to get them back or replace them, the only response he believes is justified is to continue to hurt those he sees responsible. Frankly, this type of narcissistic rage does a lot more to justify Punisher’s actions than a large amount of unprocessed grief.
While the Punisher has always been a somewhat problematic character, his psyche has been the subject of much discussion. What’s clear is that Frank Castle’s behavior and pathology make a lot more sense if he didn’t love his family as a family, but rather as the objects of his desire when he returned from war. Robbed of this much desired comfort, the Punisher became the vindictive and murderous vigilante audiences recognize today.