Ames posits an interesting theory for the large-scale arrival of the workplace and school rage shootings in the US since around 1980 - many many more than we hear about in the UK. The slang term in the title derives from the early incidences of the "genre" in the US Postal Service - not the peaceful Norman Rockwell image of the past, but instead a hotbed of authoritarian management and bullying. Ames sets out his thesis:
1. That people are inclined to do what they're told by those in authority, however nasty the regime from our current standpoint. People are conditioned by their current context, so that things we now regard as inhuman were once perfectly acceptable to most people. He adduces the relative lack of revolt against slavery in history, and especially in the US, as evidence.
2. That revolts have tended to be led by people who reacted badly to the prevailing context, and were regarded then (and sometimes even now) as mentally unbalanced.
3. That the change in US employment and school culture since 1980 - a consequence of Reaganomics, which persists to this day - has led to a vicious downward spiral in the lives and living conditions of most people in the US, and huge polarisation of society into a small number of have-lots and a vast horde of have-nots. The US people have passively accepted the ripoff of their lives by the plutocrats as the new normality, and have forgotten that life was once a lot better - and, in real terms, materially richer and more egalitarian - than it is now. Which is why the dirt-poor still vote Republican (mugs!).
4. The pressures of modern US life have led to (fundamentally doomed) revolts by people who can no longer take it: and, despite the media's "random killer" tag, the revolts are against the company/system, with intent often being to extract revenge on individuals perceived as responsible (e.g. managers, bullying jocks in school). There is often some sympathy for the killers, who may have been let down by the system (brutal management, bullying ignored in schools), but this is largely ignored in media treatments.
This is a very interesting and (to me, anyway) original take on this issue. One could see it being most unwelcome in America, since possession of any leftist/collectivist (in the broadest sense) views marks one out as un-American; with the American Way now apparently defined as enriching oneself regardless of the impact on anyone else. The collapse of trade unions (admittedly, with a helping hand from criminal infiltration) means that the working poor have pretty much no voice, so that the ruling sauve-qui-peut dynamic has few checks. And the outcome of this internally-focused self-serving is that people die.
This may or may not be the complete answer: but it's a compelling argument, and, really, you should buy it and read it.