[WS:] I suggest you read Jack Katz "Seductions of Crime" http://articles.latimes.com/1989-03-05/books/bk-86_1_jack-katz
"Katz's claim is that criminals seek not material rewards but the sensual experience of the crime itself. The adolescent shoplifter, for example, savors not the trinket she steals but the challenge of sneaking it past the clerk, the thrill of having outsmarted the system. With stickup men, as with members of adolescent street gangs, it is the transcendent joy of dominating an adversary. With the impassioned killer, it is to vent the rage triggered by humiliation or by a threat to some cherished moral value."
See also: criminology.fsu.edu/.../SeductionsofCrimeJackKatz.ppt
I would imagine that shooting a fire arm evokes similar emotions - those of power and invincibility that comes from dominating an adversary. Of course, for the great majority of people it ends with just that - a short lived thrill - after which they go back to their homes and offices and live long and normal lives. But a few less stable or deranged individuals will carry that thrill further.
I am not saying that guns cause this kind of emotions, but rather that they are one of many things that trigger them. I recall taking part in a few demos where people demolished cars and other property or fought the cops or counter-demonstrators with sticks and stones - I noticed a sense of thrill, empowerment and invincibility I experienced from merely being a part of such a crowd. Holding a rock or a stick elevated that thrill to a much higher level - the fact that you could use that rock or that stick to dominate your adversary (a cop or a member of a counter-demo) was a source of enormous motivation to keep going even if from a rational point of view the potential cost of "going" was very high (injury, arrest or both) and potential outcome rather low. (PS In all cases, I could not get close enough to the action to actually use these implements, but being a wuss I wonder if I that inability was not a form of a "Freudian slip".)
I do not think any rationalist arguments can adequately address the emotions evoked by the acts of dominating an adversary - regardless of whether such acts are real (such as breaking the law or physically attacking someone) or symbolic (e.g. shooting a weapon or watching an action movie). I think such emotions are in every one of us, we only handle them differently. Some (including myself) try to suppress them and subject to rational control, others (probably the majority) relegate them to the realm of fantasy and enjoy them by engaging in symbolic acts (watching movies, playing video games, or shooting weapons), and a few cross the socially acceptable line and enjoy them by engaging in real life acts (be it riots, gang violence, or mass shooting.)
-- Wojtek
"An anarchist is a neoliberal without money."