You may be correct. Although, it seems like the government would have moved to shut down these sites already (surely they’d find sufficient cause to do so, “freedom of speech” notwithstanding), rather than just monitoring the sites, if they thought that they do more harm than good.
But yeah, it may be better to cut off one of their major forms of communication.
The World News Network
http://w-n-n.com that I referred to in the article was shut down just yesterday and it was hosted by an American firm. Today it is up again and hosted by a Malaysian firm, so yes the government want to shut those down when they can and when they know about them but the government has to much legal obstacle to shut down a website than just regular folks sending e-mails or calling the internet hosting firms and ask them to shut down the terrorist websites and forums.