What's the Point
I can appreciate the political and perhaps emotional motivation that brought about this decision, but from an intelligence and security perspective it makes little sense:
The Internet has become a powerful tool for terrorism recruitment. What was once conducted at secret training camps in Afghanistan is now available to anyone, anywhere because of the Web. Chat rooms are potent recruitment tools, but counterterrorism officials have found terrorist-sponsored videos are also key parts of al-Qaida's propaganda machine.
YouTube is in our own back yard and keeping an eye on what training, instruction, discussion or messages are being promulgated therein was a trivial exercise. Now the producers and promoters of such content are forced to use other systems; systems probably more difficult to find and monitor. The CT business just got that much harder.
But hey, it feels good, so that makes it OK.