I don’t think this is a good idea. Yes, I hate the fact that they have a tool to spout their rhetoric. But in their boastfulness, these guys post things on their sites that can give valuable clues to intelligence agencies.
I agree....No one knows what kind of intel they have picked up.
There was a Internet terrorist guru called "Irhabi 007" or "Terrorist 007". The British government was tracking him for 2 years and they could not get him, finally they were able to get not by getting his IP address but by arresting 2 other terrorists who knew him.
Shutting down the terrorist websites and forums will make the terrorists deaf, blind, and mute and that is vastly more beneficial than any little information we can get from them on the internet.