Fantastic article. I imagine this has been a problem ever since the first canon's were invented. Something that could kill people far away that you can't actually see. The one thing you don't mention is how often we have "friendly fire" or "blue-on-blue" if you're British, without unmanned drones.
I think the hardest thing facing soldiers today is that they seem more a police force that an attacking military group. When a soldier in uniform faces another soldier in uniform, there's a complicity in trying to kill each other. When one of those combatants doesn't wear a uniform, but dresses as a civillian, then that's when the psychological toll seems to start. Your enemy can be anyone around you. You are constantly on alert. You mistrust everyone (including your allies who may be insurgent infilitrators). I feel pity for the modern soldier. It doesn't excuse it but it certainly explains why armed forces are pushing the envelope of an "ethical" war.
The more horrifying thought to me is that there's insistence that there is this "enemy" against western society particularly in Middle East and Islamic countries. I know there is, but it's not everyone in those countries. And for every bad guy killed, there's probably 15 friends or relatives, who were largely indifferent to the west, who will now hate us and wish us death. The more you kill, the more enemies you create. That's why capture and trial, difficult and messy as it might be, shows mercy, and a sense of justice.
It's the usual problem though of principal versus practice. The law in the west is based on the principal that it's "better that ten guilty persons escape than that one innocent suffer" is being completely ignored in our current "wars". The idea is that it's better to kill ten innoncents as long as we get one of the guilty.