That is a much more complicated story - even without our input there are huge factional issues across the middle east and Syria was a problem waiting to happen - there was no way all the different elements that ended up there could have been reconciled. I can't remember the exact figures but a fairly moderate proportion of the population there ended up there as refugees in the first place.
Then let them happen why wade in and paint ourselves a target?
Isis is goading the west to attack them, this was apparent since they killed the first American hostage. It didn't gain them anything but missiles.
Missiles that took lives, more fuel for there cause.