Don't the people that the terrorists need to recruit use Skype, and GMail, and Facebook? Find the recruiters & PR types that have to be where the people are, and that's one more in you have with a nascent terror cell.
Indeed. If the objection is that people drop off the easy to see communication systems and start having more shielded communications as they radicalize, then the objection carries within itself a description of very pattern that one can use such a internet traffic surveillance program to search for.
A naive version would generate plenty of false positives, but following up on random entries in the list generated would quickly reveal classes of other reasons that people's comms go dark (having children, new job, moving to a new town, major injury or illness, depression, etc.), and one could start filtering using that. Also one might get some use out of looking for clusters of people going dark in various social-connection graphs, and commonalities of what people fitting the comms-going-dark pattern read and say online.
