Re: “ISIS has nothing to do with Islam”.
We need a decision tree for this. If the person is non-Muslim, and convinced they are, then nuts to them. No further effort should be required, we should NOT do the public penance thing.
The more important target are those Muslims who are on the fence or supportive of ISIS. We have a rich history dealing with such types, (Khawarji), not to mention that central tenant to ISIS belief, that Qayamat can be brought about by acting out prophecy, falls flat with predestination.