Don't be dismissive at the idea of radicalisation online. We live in a world that is basically connected 24/7. We're influenced by what we see and hear and it's not completely out of the realm of possibility for someone who does feel disenfranchised or treated as an outsider to see attacks on Muslims in other countries by "the west" constructed and presented in such a way to turn someone moderate in their beliefs into radical if they see themselves and their beliefs as being under attack.
I was discussing with someone today about the whole shift with "extremist Islam" and he made the point of, firstly, what do these people really want? We knew what the IRA were after, we knew what the UDA were after, what do ISIS actually want?
Secondly, what caused 9/11 and the whole shift in perception? What led up to it happening? What led to people to take that step and bring "radical Islam" as the new enemy?
(I'm thinking out loud/on forum at the moment, trying to really figure out what the hell is going on)