What I would say is that ISIS is one of the more horrifying consequences of everything that has happened since the neo-cons saw an opportunity in 9/11 to manufacture a dishonest case against Hussein to justify invading Iraq, setting off all the chaos in Iraq and Syria ever since. Yes, the dictators of Iraq and Syria were/are brutal men who had the blood of thousands on their hands. But the actions of the US have caused the death of many hundreds of thousands by comparison, along with millions of refugees and the horrors of slavery such as are described above, and much other devastation besides. This shows how badly neo-con imperialism can and does go awry.
People knew ISIS was coming. ISIS staged a massive invasion. Why weren’t the staging areas etc questioned? Why was ISIS allowed to deploy in an obvious assault? ISIS military functioned because Sadam’s generals were involved, many very capable. Then ISIS was allowed to exploit oilout of their region. Obama refused to bomb tanker convoys carrying ISIS oil. ISIS could have been stopped in their initial advance but Obama refused. Then ISIS could have been strangled but Obama refused. Why?