A short, detailed article based on an interview of Professor John Horgan, a British psychologist now @ UMass-Lowell:http://nymag.com/scienceofus/2014/08...-recruits.html

A key point:
They’re offering an opportunity for people to feel powerful. They’re making disillusioned, disaffected radicals feel like they’re doing something truly meaningful with their lives.
Are we and others ready for this?
Disillusionment is very, very common in every single terrorist and extremist group you can think of. That’s something that can be very toxic if those accounts get out and gather momentum.

Disillusionment is the most common reason why people voluntarily choose to walk away from a terrorist group. People become disillusioned if they feel that the group has gone too far, if they don’t seem to have a strategy beyond indiscriminate killing. Disillusionment can arise from disagreements with a leader, it can arise from dissatisfaction with the day-to-day minutiae. There are many directions from which disillusionment can arise, and it’s only a matter of time before those accounts leak out from ISIS, and I think we would do very well to be on the lookout for those kinds of accounts, because they offer an opportunity to dissuade further potential recruits from being involved.