Our culture has a lot of issues. A good book to read is Terror at Beslan by John Giduck, or pretty much any book written by
LTC David Grossman, with particular attention to the book Stop Teaching our Kids to Kill.
We are essentially conditioning our children to be apathetic and indifferent to everything, including violence. We glorify violence in pretty much every aspect of media, from TV and movies to video games and internet videos.
With particular reference to the mentally ill, we have a lot more recognizable mental illness now. This is exacerbated by medication and self-medication issues, of course. However, this issue is also made worse by the media that is available. You take someone who is already experiencing an extreme schizo-affective disorder, narcissism or outright schizophrenia, and you show them TV shows like Doomsday Preppers, or the myriad of shows about the end of the Mayan calendar, and now you've basically poked and prodded someone already on the edge and pushed them over that edge.
Look into the ghettos or "urban" communities where kids are taught from a very young age that materialism is the most important thing in the world, and that nobody will respect you if you don't have money, bling and a hot ride. These are kids who, if asked what they want to do when they grow up, will either say they want to be a pro athlete or a rapper. Nobody wants to be a doctor, lawyer, pilot or train engineer. They are inundated with influence from the only thing they see, which is the "urban" culture that glorifies irresponsibility, materialism and violence. Their role models are generally gang bangers who teach these kids that respect is earned through violence, killing, dealing drugs and disprespecting women.
Next, go to suburbia where kids are glued every waking hour to their Xbox360 or PS3. These kids will literally go up to a combat veteran and tell the vet all about war, just because they've played Call of Duty. They watch actual war footage on YouTube and all they do is go "COOL!" Completely desensitized to violence.
Or, take any kid aged 12-19, and look at how every aspect of their life is inertwined with Facebook and Twitter. The term "cyber-bullying" had to be invented to describe the amount of emotional anguish kids are experiencing because people talk crap about them online.
We have messed up laws and a legal system that is designed to prevent people from being held accountable for their actions. There are felons who have been arrested multiple times for possessing a firearm (felony in every state) that keep getting put on probation, likely followed by double-secret probation. Over and over. Yet, a law abiding citizen who neglects to pay a $200 tax fee so that they can take 1.5" off the length of a rifle barrel will face 5-10 years in federal prison. Data privacy laws protect sex offenders, as most sex offenders are not assigned risk levels (Level 1, 2 or 3), so most of their neighbors don't know they're convicted sex offenders. Etc etc etc.
We have a significant problem in this country, and so much of it is based around people who simply have no incentive to take responsibility for their own actions. All we do in this country is try to find ways to explain or justify things, and find ways to eliminate capabilities. Look at prisons- they're "rehabilitation" facilities. Prison is where you send someone to be contained because they cannot function responsibly in society, but we try and soften that because we don't want to treat criminals like criminals.