No matter how any of us try, we will not achieve any understanding the thinking behind such acts. Watching bbc news they were talking about surfing affiliated terrorist social media sites for info. I might be being naive in this modern SM age, but I can't for the life of me understand how they can have affiliated SM sites? Should these not be shut down immediately they are found?
There are two problems with shutting down Social Media sites, that's if they are sites and not just groups on FB etc. The first is how easy it is to set one up and just how many groups there are on Facebook etc. If you shut one down another can spring up almost instantly. The same goes for websites. You can host them off the back of anything and mostly hide them. Shutting them down is like playing wack-a-mole.
The second issue is a little more cerebral. If you know where they are and you can get a list of the members and people using them then, as the security services, that's a great tool for tracking down these people and dealing with them prior to any act. The danger here though is that if people find out that you know about such groups/sites and don't manage to stop one attack by a member then are you culpable. Tricky.
I know that the government want the SM sites to police their own content, but that potential makes them liable to what is on there, which is the equivalent of making the post office liable for everything that's sent by post. In the mid-90s the chief way of distributing dodgy stuff was Usenet groups. I worked at a major ISP at the time and we, along with all the other ISPs, got a message from Special Branch telling us to drop a number of these newsgroups because the content was illegal. My company chose to do this, some of the others didn't because of the liability issue, and also getting a feed from outside the UK wasn't that difficult. My feeling is that prohibition rarely works, better to educate and prosecute.
There are measures in the recently published Tory manifesto that say that they are planning on controlling the Internet. I'm hoping that they won't try to make political capital out of this once the initial horror has died down.