From my perspective I'm afraid that none of it is fine. I don't care what the motivation and how ISIS try to justify their behaviour: it's just not OK. I know that's my judgement, and I'm not God, so perhaps it's pretentious to judge, but when a massive sector of the world's population feels revulsion, I have to conclude that we are all witnessing and recognising evil in its purest form.
So, that's the judgement handled. But what is the learning from this? At one level it is challenging my internal need to know all the answers and how things should be. It is also challenging the part of me that wants to be God by demanding that everything should be fixable, because right now, although I demand that things be different, the truth is that I'm not sure that this evil is fixable other than by imposing a new type of evil on it. I'm not in the least convinced that one form of violence can be fixed with another type and we can somehow judge one type of killing to be "evil" and the other "good".
At another level, it seems to be inviting me to let go of my revulsion, to let things be in the sense of not judging good and evil, but rather to accept that things are as they are right now. Perhaps we are being invited to stay in touch with our humanity and to remain open to and explore possibilities other than more war, more killing and more antagonism and resentment.
The truth is that I don't have a clue what the solution is, but if it can somehow flow from our inherent and common humanity, that would be a far better fit for me than violent retribution. Perhaps forgiveness is a piece of the puzzle. Perhaps love is. Perhaps saintliness will also play a part. Isn't that what Jesus' crucifixion was all about? There is an echo of similarity here.