why?
if you live in a country that extols war without reason, who's values are simplistic black and white goodies and baddies, even more so as it desperatley defends its position by painting everything in really really polarised terms because there seems no other choice, then surely there will be people, especially young people who will internalise some of this state sanctioned violence, internalise it and turn it's values as personal war. It's certainly not an unusual thing in the US and as a reaction to the US in many ways historically, i'm not just talking about guys with guns in schools, you could take in the panthers, weathermen, timothy mcveigh etc, even though we know about how they internalised and justified their personal wars, they were undoubtedly a creation of US culture and usually one at war. Painting the person who did this as just a lone random crazy avoids all the factors that go to create this situation, and doesn't help explain why it keeps on happening in similar US instituitions too, those that try and fill people with some types of the values of US society.
I can't help feeling you're just projecting your own political grievances onto a situation that has nothing to do with them. Clearly the US has a problem with this kind of beheaviour, though it's by no means exclusive to the US - just worse.
Here's a chart I've seen of random massacres of more than 10 people dating back 40 years. Note the appearance of Switzerland and New Zealand, neither of them countries "that extol war without reason, who's values are simplistic black and white goodies and baddies" I'd say. Note also the absnence of Russia, a highly militarised country which has considerable experience of simplistic views.
http://www.gun-control-network.org/GF02.htm
26 Apr 2002 Erfurt, Germany 16 + 1 Legal guns, pistol club member
27 Sep 2001 Zug, Switzerland 14 + 1 Legal guns, licensed pistol owner
29 Jul 1999 Atlanta, GA, USA 12 + 1 Legal guns, no licence required
20 Apr 1999 Littleton, CO, USA 13 + 2 Not legal guns
28 Apr 1996 Port Arthur, Australia 35 Not legal guns
13 Mar 1996 Dunblane, Scotland 17 + 1 Legal guns, pistol club member
16 Oct 1991 Killeen, TX, USA 23 + 1 Legal guns, no licence required
13 Nov 1990 Aramoana, New Zealand 13 + 1 Legal guns, licensed gun owner
18 Jun 1990 Jacksonville, FL, USA 9 + 1 Legal guns, no licence required
06 Dec 1989 Montreal, Canada 14 + 1 Legal guns, no licence required
19 Aug 1987 Hungerford, England 16 + 1 Legal guns, pistol club member
20 Aug 1986 Edmond, OK, USA 14 + 1 Legal guns, no licence required
18 Jul 1984 San Ysidro, CA, USA 21 + 1 Legal guns, no licence required
01 Aug 1966 Austin, TX, USA 16 + 1 Legal guns, no licence required
I'm really interested to know why these things keep happening, seemingly with greater regularity and ferocity. Why do they invariably seem to be middle-class losers/loners?