I'd say Fight Cub illustrates it very well. Just compare the protagonist's social life before the movement (he knows no one, he's doing very strange things for companionship), and all the friends/followers he has during it.

As for the in-group: I'm not sure it fits. The surveys cite friends, remember, not specific grievances. And the waves of recruitment to al-Qaeda such as the 9/11 one seem to follow humiliation of out-groups. This fits with the social model - al-Qaeda has become of higher social status, and possibly safer to join - but not with the feel-better model. 9/11 made them feel better! Why would they join after feeling better, instead of joining before to contribute to feeling better?

Fight Club demonstrates this perfectly (even more perfectly in the book, when it's made clear that the main characters entire goal is to get a woman). Men who feel pointless, empty, marginalized by the system they live in are willing to do anything to achieve high-status and a sense of purpose. This so closely resembles terrorism that I would be more interested in terrorist groups and acts that can't be traced to some sort of status or purpose-seeking, as I imagine they are few and far between.