Since all of Arab culture is so incredibly dysfunctional and based on lies and image and bluster over facts, it's important for these people to experience first hand who the real enemy in Fallujah actually is. Hint: they aren't wearing the Stars and Stripes. Telling them this six hundred billion times doesn't work, but showing them once by leaving the city alone so they can spill blood on each other is sometimes the only way.
Ya, know, the Iraqi's can just take on Falluja as a project, themselves, we freed them from Saddam, now they can go in and root out the resistance, and if they cannot handle it then, too bad, they will have to learn how to fight for freedom, it doesn't come with cost.