What I mean to say is, you are speaking as if the problem was just with psychopaths. But every nation has mental cases that would commit these atrocities.
Then we see that it happens a LOT more often in the US than elsewhere. So logic dictates that the reason must be either..
a) America is generating a larger ratio of mental cases.
b) There is a major difference between America and other countries that makes committing these atrocities more common.
A) seems very unlikely. Mental issues are exactly that, mental, and the number of crazies in the population will be pretty balanced all over the world.
So that leaves B). Now B) doesn't necessary mean it's because guns are massively easy to obtain compared to the rest of the world, but that's the biggest possibility. Whether it is a lack of gun control or something else, we need to find what it is, and eliminate the problem.
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.