You don't see Danes or Australians or British or Germans or Canadians committing such atrocities in such large numbers with anything approaching the same frequency, so I suppose it's logical to assume that, somewhere deep in the "American soul", there's something dark and twisted that isn't as prevalent elsewhere in the world. Leaving gun laws completely aside (because crazy people will always find a way to inflict cruelty and misery, method being irrelevant), the question needs to be asked - what is this dark stain on the soul and why don't we see it elsewhere?
Don't get me wrong - I like America and the Americans I've met and I do not wish to tar all 300 million of them with the same brush. I just look at all the shooting sprees, insane fundamentalists like the soldier-hating, funeral-picketing Westboro Baptist Church and those who murder abortion doctors (and the considerable power & influence of the fundie religious right in general), the large numbers of insane cults (see previous), the world-beating serial-killers, the over-the-top nationalism, the constant wars, the (still!) overt racism (in some parts), soul-darkening things like lethal injections and electric chairs and think "what the hell is wrong with this beautiful country?" I feel sorry for normal, everyday, moderate Americans who think the same things but can't mention them because they'll be branded 'unAmerican' (whatever that is).
If you're American, don't take that as a dig at your country. It's an observation from someone impartial. It's a perspective a lot of people share and it's not just about what happens in the US. The negatives about America invariably seem to be expressed by whoever's in charge at the time, which always impacts the rest of the world. We've had 8 years of macho, faith-based posturing, misgovernance and hideous violence that's affected the entire world and I think some of us may be worried that there's still room to slide further downhill. Every time another shocking story like this latest shooting emerges from the US, we think "what the hell is going on over there?"