I have to agree with Teribus.
When 9-11 occurred, we had no idea who was behind it and, yes, we were in criminal investigation for years because of this ambiguity. But where's the ambiguity here? These people have claimed responsibility for murdering 100 plus French citizens. And killing 40 in Lebanon. And taking down a Russian jetliner. What does it take to provoke us into taking decisive action?

We know who they are, where they are, and why they did it. Sure, we don't know all of the reasons and causes and things we could have done better to have avoided this situation. But when the Titanic struck the ice berg, I don't think time was set aside for a period of mourning, and followed by a careful analysis of the ice berg patterns in the North Atlantic. It was time for immediate action.

In perhaps a more accurate analogy, Daesh is like a cancer on the face of the world. Once it has been successfully diagnosed, there may be time for anger and for sadness, but the task at hand is to eradicate it before it spreads, if our own survival means anything to us.

Kindness, peace, and understanding between me and my fellow man is something I fervently desire. But when someone has professed a desire to kill me, self-preservation takes precedence.