First I absolutely hate ISIS and what they stand for. But for me it is understandable how extreme or fundamentalist groups of people with aggressive and very conservative agenda can gain power and influence when the moderates collapse or are decimated by decades of poverty, war, sanctions, economic decline, high unemployment, occupation of your country or a neighbor country by a foreign power, etc.

After all, the good "guys" are more or less the same in every country. They are the ones who flourish in good times e.g. intellectuals, professionals, scientists & engineers, students, teachers, artists, diplomats, businessmen, journalists, entertainers, etc. Those people mostly contribute to and profite from peace and tend to elect moderate politicians.

But in time of hardship, those mentionned above lose influence. The right gains. In very desperate times the extreme right wing tend to dominate. ISIS is a super extreme right wing backlash to decades of horrible and inhumane condition in the middle east.

In Europe we went bonkers for less than that (e.g. 2nd WW and the Holocaust)

So I hate what they are doing but I think that it is understandable and actually a horrible but normal human reaction to extreme suffering

edit: Like how we did in Europe, Japan and South-Korea, I think investing fucking heavily in those countries, their moderate citizens, their education and businesses to rebuild them, while prosecuting all terrorists will heavily weaken and reduce in numbers those extreme right wings.

Seriously have a look of how MacArthur and others have dealt with post war Japan. This is how we should have treated countries like Somalia and Libya instead of letting them fail and become a breeding ground for terrorists.