Contagion theory could explain violence

Once a culture latches onto certain ideas, they can become deeply entrenched over time.

Jasper Johnson

A man with a gun walks into a school. A young woman detonates an explosive belt in a bazaar. These are stories we’re all too familiar with, and they seem to have emerged out of nowhere. 
I believe suicide, shooting sprees and suicidal terrorism are all unusual forms of violence that latch onto the public psyche and become embedded in our expectations of human conduct. This leads to the sudden “contagious” emergence of certain patterns of violence, which spread like a disease as we circulate stories about them. 
For example, firearms did not suddenly become deadlier in the past few years, causing an uptick in shooting sprees; nor did humans recently develop the means to strap explosives to themselves. Perhaps something happened to our cultural narrative of violence that led to these phenomena. 
For lack of a better term, I call this development “contagious violence.” By contagious violence, I mean certain types of violence come into the public eye and are further replicated by others who follow a new norm, consciously or otherwise. It’s almost like people read the news and say, “This is a thing we do now? OK.”
From what I observe, when stories about mass shootings permeate, we are left with a society that embraces the notion that when someone goes off the deep end, their course of action is to gun down others in a killing spree. 
The same occurs with terrorism — extremely deadly suicidal techniques have apparently become an expected norm globally. They are now a standard tool for terrorists. 
Still, I’ll admit my theory isn’t perfect. For one thing, suicide bombings have occurred at least since the Algerian War in the 1950s. Also, the rise in mass shootings is an issue, but the numbers are often wildly inflated through lenient definitions.
Furthermore, when I consider how ideas of violence spread, I’m left with more questions than answers. I’m also completely baffled as to the policy implications of contagious types of violence. 
Some say we could address the issue by changing the ethics in how we report news on violence. This is well-documented with patterns of suicide. Because certain types of headlines and characterizations can lead to a domino effect of suicides in a community, journalists have complex ethical guidelines for how to report on a suicide. 
Some people try to extend this logic to spree killings or even suicidal terrorism, but I think that ship has long sailed. We as people cannot unlearn the existence of these types of violence. Also, it becomes even harder to control the hysteria of coverage now that social media is so prolific.
To address spree killings, I think the answer to their prevention lies somewhere in contagion theory. However, I don’t think we’ll shake the trend of mass shooting anytime soon, or suicidal terrorism for that matter. 
In any case, thinking about how these patterns of violence spread through society may provide a clue as to how we can stop them.