Why do they go? Why do young people from America, Great Britain, or any free country take themselves to the Middle East, to live and act worse than animals, and perpetuate evil for the further "Glory of Islam".
Most of these people had decent lives. Many seem to be of at least moderate intelligence. I doubt they are moved by intense religious fervor in spite of their claims. If they were doing it for the adventure, they could better be backpacking through Asia. Looking at the people they are joining up with, I doubt they are doing it for the good fellowship.
So why? My suspicion is that if these people were to watch the TV show, "Criminal Minds", they would root for the serial killers. I believe that these people are hard wired with a vicious streak and by joining the jihad they rid themselves of societal constraints.
Why would anyone, not thrilled by the blood and pain of others, even consider such a life. To be able to kill, rape, and behead women and children without remorse you have truly lost your soul.
They claim a religious duty to Allah. They claim, not just the approval of their deity but that deity's promise of an afterlife of glory with seventy-three, or some ridiculous number, houris to serve their every desire. No sane person would believe that tale out of "Arabian Nights".
However, not every jihadi convert is a genius. I think that we can all accept that fact. So their new masters take the slowest and most needy and convince them that the fast track to glory is to strap on explosives and go blow up a bunch of innocents at some mall or restaurant. Now my reading of the Quran is not terribly extensive, but I know that the killing of innocents is contrary to Islam. I'll bet those youngsters are well surprised when they find themselves stoking the fires of hell rather than being served by comely young women.
So by their going to the Middle East and practicing mayhem there, we are saved them going on a murderous binge in their home countries. What we need to do is to take their passports away when they leave so that they can never return. Then we must track them to there final destinations. Then put those destinations on the flight plan of a future Predator strike. The world will be a better place without them.