I don't see any argument or evidence for the assertion that people who engage in atypical levels of violence have atypical personalities. We would expect sociopathy to be a factor in making someone more prone to violence, but there's no reason to assume it would be the sole or most important one. Most people, most of the time, don't find themselves in circumstances where the benefits of violence outweigh the risks. Even when a person finds themselves in a position where violence might benefit them, they have to weigh their own ability (probably untested) against the challenge (probably unknown) and may wisely decide that this is not the right moment for their rookie attempt. But someone who has previously tried and succeeded, or who has prevailed when attacked by another, has a more informed basis for choosing violence in a given situation. If it goes well, it may make them bolder in a subsequent situation, and then another, etc. And we might see this person as having an atypical personality, when it is only that they had some early experience that tipped the balance towards making violence a more rational choice for them.

As engineers, we can see in our own practice that an early job experience that led to us master a particular technology makes us much more likely to reach for that technology than we would if we did not already know it.