This is just my opinion and you may call me crazy for thinking so, but the US has a strange breed of mental, in many different definitions. I think in recent we have seen more people snap because of economic issues, leading those that were good to go way out to left field and the part I'll probably get some flack on is that 21 December is coming up (this is only for the elevated recent events) and I thnk some of these people are truly convinced its the end of the world causing them to snap or at least go public with there issues thinking they have nothing to lose. I travel a lot and can definitely see the US is an odd breed. For a lot of people, they do not know how to handle lesser times and they can't cope.
I won't every attack anyone for having an opinion, but honestly, I can see your perspective. America has a lot of extremists, whether they are religious, political, or social. But realistically, I too have spent a lot of my short life travelling, and I can happily say that America has it easy. You're hardly living in a third world country. If it was just "The End of The World," it wouldn't have been going on for so long. There is another reason at work here, I really can't see the reason for all these massacres as "America generates more psycopaths."