While I don't doubt that ISIS is from the pit of evil itself, I do believe that they are being allowed to serve more than to full on believe that they are serving God (allah to them) by abiding by what their disgusting quran promotes. Just like in human history where mass murdering took place and it was forcefully accepted or you die too, they all tie on the fact that it decreases the general population by taking out civilians and soldiers alike, making it more like a human population control despite that we're 'at war with ISIS'. Can't we say the same about there being a mass 'genocide' and false information for when it comes to abortions and how they process? Besides, why bring in so many more faces than what we have now if we fear of lacking the resources to provide for them all?
Mind you, I don't agree with the last bit even though I get convinced that there's too many people walking around (being the antisocial that I am anyway). But it's pretty much how it's ran. Maybe the ISIS members solely think they're serving their god when reality is they're helping those who cooperate for mass destruction to occur in the first place.
