I don't like that this happened but speaking as a former soldier I'll make a few points. First, in this particular war, it seems that due to certain terrorist actions that these soldiers have a right to be wary of ANYBODY approaching their checkpoint. It's not like their military has given them a choice in moral judgement versus self-preservation and the safety of those that they're guarding. Secondly, as a guard you have strict orders that tell you explicitly what to do in all situations. Failure to do these things could result in not only comprimising their own life but also the lives of those within the camp and possibly the loss of resources, ordnance, intelligence, ect that the camp may contain. These aren't mall rent-a-guards. These are military members doing their duty exactly as instructed and as many Iraqi citizens have grown up in a more militarized society than most Americans they realize these realities more so than most Americans who are appalled
by their actions.