The Shi'ite militias that resist ISIS, where the Iraqi army is incompetent to do so, hate Sunnis and intend to expel them from any areas they capture from ISIS.

This is likely to force Sunnis to support ISIS even if they detest ISIS's oppression and cruelty. Unless they have somewhere else to turn, and at present they don't.

US Republicans want the US to intervene against ISIS in Syria.

I don't think the killing of one US journalist, on top of so many others murdered by ISIS, is particularly important. I don't think ISIS is close to attacking the US itself. Whether this sort of intervention is right depends mainly on its effects on the region itself. I can see the reasons in favor, but I also worry that things can go wrong in ways we are not likely to anticipate.

US military support for Kurdistan makes sense because Kurdistan is a nation fighting a conventional war. It has an army that is loyal to something more than its pay. In addition, Kurdistan is not likely to fall into brutality comparable to that of ISIS or the Shi'ite militias.

The use of drones to attack ISIS poses no special ethical issue because the targets are military units, typically equipped with unmistakable military vehicles or heavy weapons — not cars, houses and groups of people standing around, that might well have civilians in them.

Can/will Kurdistan protect Sunni Arabs that wish to join it? Can it offer them a way out of support for ISIS?