“Sun Tzu’s The Art of War strongly emphasizes the use of flanking, although it does not advocate completely surrounding the enemy force as this may induce it to fight with greater ferocity if it cannot escape.[3]”
http://en.wikipedia.org/wiki/Flanking_maneuver
With respect, we are not trying to politically demoralize this enemy. We ARE trying to destroy them, and a fully surrounding maneuver, no matter how hard it makes them fight, allows each last one to be killed without the possibility of living to fight another day.
I say push them out of their territories as quickly as possible, and when they are all herded into their last stronghold, surround it on 4 sides and firebomb said stronghold into rubble like Dresden, and kill any thing that crawls out bleeding from the rubble.
This is a chance to eliminate a whole lot of psychopaths and sociopaths who have flocked to enjoy raping, beheading, and burning those with different opinions. ISIS/Daesh fighters have spit on Geneva Conventions and will pay the price if others succeed.