Let me be clear here. I'm very much against guns being as prolific as they are. The bullshit defeatist "if guns are illegal, only criminals will have them" argument is so abundantly wrong-headed it defies belief, IMHO. Just look at the gun statistics in England compared to the the US and you have a compelling argument.
When you're looking for reasons why one society in particular has a record of atrocities like this, the first place to look is what makes that society unique. The famous NRA quote "It's not guns that kill people, people kill people" was an attempt to deflect criticism of the penis-extensions^W^W guns generally available (to which my and Eddie's retort is "sure, but the gun helps!"), but like all good propaganda it contains a kernel of truth. The real question then is "why are these people killing each other ?"
The real reason people are using guns to kill themselves and others is the society that they live in. The cold hard truth is that guns are available worldwide, and yet it's a peculiarly American thing (with some outliers) to go crazy and kill a bunch of children/people using your personal arsenal. What's wrong is deeper, I believe.
IMHO American society is in a slow but inevitable death spiral...
- The prevailing cry when social healthcare was proposed goes along the lines of "why should my tax dollars pay for your healthcare"
- The attitude that it's "every (wo)man for themselves", and you get ahead by screwing others. Sit up at the back there, Wall St.
- The violence inherent in the main sport - American football is more about the crunching tackles than any skill.
- The "jocks" vs nerds attitude embodies the whole "might is right" credo. This is a society-wide meme and science is losing the popular vote.
- That corporations attempt to squeeze every last drop of blood out of the stone, leading to a significant erosion of the medium skill tiers, with more low-paid, low-satisfaction jobs to support the higher-ups without providing any competition to them
- An ever more militaristic police system. Tasering, SWAT teams, armed police everywhere. It's just bad.
- The highest incarceration rate in the world (743 from every 100,000). Worse than China. About 80% of those are "Christian"...
It's hard to reconcile that Americans give generously to charities with the first two points above, unless it's just Democrats doing the giving; which is unlikely :). I'd have to posit a discontinuity between the act of giving, and the way of living. It's as if people are ok with being nice to others if they choose to, but refuse to have the general good of society imposed upon them. That's a very odd form of independence, and smacks of biting off your nose to spite your face, but since I don't understand the motivation, I may have it completely wrong there. What's clear is that charitable donation is important to Americans, but charitable society is not.
Religion also plays its part. The society is highly religious, relative to the developed world but religion here in the US is a business like any other. The prime goal is not to try and guide society in the right direction, it's to funnel cash to the higher-ups in the religious power structure. People are told they're doing the right thing as long as the cash is flowing upwards,and the "church"'s goal is simply to continue to make sure that is the case. Upon examination, it's a good metaphor for what's wrong in the more-general society.
It adds up to an uncaring society, and I can see how anyone stuck on the lower rungs with seemingly no prospect of getting higher up could reject it, and similarly reject the rest of the social rules we all expect to be obeyed. There's no golden solution here, no panacea, you're not guaranteed anything will ever be perfect, but if the society had more general welfare built in, it's my personal belief there'd be less atrocities.
A society is by definition a group of people collectively living by a set of rules. Ask any evolutionary theorist what's important, and (s)he'll tell you it's the rules of the game and the boundary conditions imposed by the environment. The environment in the USA needs a lot of attention IMHO. It's forcing the society down some unwholesomely bad paths.
Just IMHO, as an outsider looking in. Unlike most, I'm not stuck here. I've made no secret of the fact that I doubt I'll be staying here much longer. The above is why.