Is it possible that they are already using it ?
Has anyone thought about the possibility of them using the coinbase to send messages to, or to activate Sleeper Cells in the US and abroad ?
It's quite possible that there just might be someone in a cave somewhere in the Middle East, currently able to stay in contact with operatives thanks to Bitcoin.
Should there be an Anti-Terrorist Bitcoin Organization who monitors blocks and transactions for this very reason ?
You are living in a fantasy world. What on earth would al-Qaeda want to use BitCoin for when they could use cash? Given the very few ways to cash in or out large sums and the very many ways to move large amounts of cash around any terrorist use of BitCoin would be just plain silly. It's possible to send messages from anywhere to anywhere without the massive complexity of hiding them in BitCoin's blockchain.
Stop spreading American media style fear because it doesn't belong here. Every time you get molested at an airport, or get your papers checked by some psycho who really just wants an excuse to give you a really bad day remember your irrational fear of Al-Qaeda caused you to live in permanent fear of your own government. The terrorists won and they are called the TSA.