Protecting civilians -- why it's harder than it 'should' be

Civilian deaths have been getting a great deal of attention in the past couple of years in the Afghanistan war — almost exclusively when members of the NATO Coalition inadvertently cause the death of “civilians.” 
Many times the enemy hide in the homes of true non-combatants, other times they lay down their weapons in the classic guerilla tactic.  I would hope by now that we are all familiar with the hit and run tactics of an enemy that refuses to wear a uniform or follow the internationally accepted rules of war.
The vast majority of controversy we have seen in Iraq and Afghanistan wars have arisen from the behavior of the enemy that does not follow the accepted rules of warfare.
I hate war. I have experienced it first-hand.  I have been to funerals. 
Our enemies seem to love war and the abuse of its human victims, both living and dead. These are the folks that bring us the beheading videos of anyone they can find, including American service members.  They take joy in cutting off someone’s head, showing their “pride” by wearing masks so we can’t see who is doing the cutting.  These are not freedom fighters that the Left likes to compare to our minute-men. These are animals capable of any atrocity to instill fear in the opponents.
This week the metaphorical, if not a real, line was crossed by the Taliban.  They executed ten foreign aid workers. 
“Why?” you ask. The rumor is that they were talking about Christianity to the locals. To read the testimonials of their surviving friends and family members that was not the case. These people were giving medical aid and treatment to Afghans who had never seen a tooth brush or thought to wash their hands. 
The terrorization of the local population and those that would help them should not be new in the minds of any Americans old enough to remember Vietnam.  The enemy there would cut off the arms of children who had recently been inoculated by American medics.   They did this to show the local population that the Vietcong was in charge and cooperating with the Americans was a losing proposition so don’t even bother trying, when we leave they would still be there.
If and when we leave Afghanistan, there is a good chance that there will be retribution killings going on no matter what the situation is on the ground.  The government simply cannot be everywhere all of the time. 
The authorities cannot protect the people all of the time even when we know who to look for: even here in America, two convicted killers have escaped from prison in the southwest and have killed again.
  If we cannot ratchet up the intensity of our will to kill the enemy and at the same time show courage in the face of ruthlessness, then we might as well admit that now and save the countless families who will suffer because of our impotence. 
If we cannot protect those that want to teach dental hygiene, how can we hope to win hearts and minds?