If that happens, we will then deal with what we surely would get with indiscriminate killing of civilians. Vengeance is a dish best eaten cold. We don't want to ignite a global war by acting rashly if we can avoid one. I tend to wonder if some neocons share that view.
War is a means, not an end. If we can achieve the same results through diplomacy and limited, covert engagements, so be it. My only fear, however, is that we will change our end objectives in order to avoid war at any cost. This is what happened at Munich, and it served only to postpone a far worse conflict.