This is tragic, and while its fully in the category of "it could happen anywhere" (even though its more likely to happen in a war zone), that is not how it is going to be perceived and perceptions matter. An already flawed operation will probably sink faster after this.
Still, this psycho going postal (my apologies to postal workers, I know its an unfair term ,but by now everyone knows what it means) may concentrate some minds on the fact that there IS no visible strategy in Afghanistan. http://www.youtube.com/watch?v=WdNsltQXTVU
To say (as someone in some official position already has) that we will not allow this tragedy to obstruct the mission is to get people thinking "what is the mission"? When enough people think that, the emperor may suddenly feel very naked.
I am not saying there is absolutely no strategy. How would I know? at some level in the deepest recesses of the pentagon and the state dept, there may be several strategies. But they may be at cross-purposes, thats one problem with "secret" strategies...there may be several and nobody knows what is what. With unity of command and one man (say, the president) clearly in charge, at least HIS secret strategy would have some coherence. But that is not how the system is in the US (what president since Nixon would you think of as having a devious enough mind and enough interest in foreign policy to be in that position? Clinton had the IQ, but not the interest..anyway, the problem is likely systemic and not solved by having a different person pretending to be president),so that is not a relevant model. The publicly declared strategy (building a viable Afghan democratic government, etc etc) doesnt seem viable and, more to the point, doesnt look like the actual strategy anyway. People seem to have other unspoken (publicly officially unspoken) thoughts in mind. Maybe they are "containing Pakistan" or doing some strategic bullcrap re central Asia, China, Russia, whatever. In bygone days, we might assume that the elite knows what they are doing but if you watch long enough, that doesnt seem true either. Its a mess.
On the practical matter of the POS who did the shooting, it would have been far far better to shoot him dead right away. ANY trial and ANY punishment from here on will just add to the mess.
Sometimes, there really is no good choice.