Using the rationale that "killing" ones opponents only engenders their Next of Kin and neighbors to continue the fight only holds to a very limited point. Once they see opposition is futile, hopeless, and bound for failure....they will lay down their Arms and submit....or desist in their hostile ways.
A couple of quick points on this - firstly we're not always talking about enemy combatants. Civilians have often been caught up in events. As for desisting in their hostile ways, I would point out that in the case of Iraq their forces weren't acting in a hostile manner prior to the our invasion. One could reasonably argue they were simply defending their country against an ostensibly unprovoked attack by an external aggressor. I know it was darned unsporting of them but hey, what would you have done in their position? Laid down your arms and embraced your invader?
As for my earlier somewhat ill-judged comment regarding offering resistance, what I should of said is that I nor probably most of the detainees involved have had the benefit of the training previously described.