Well if I thought of this in my "spare time", I assure you that terrorists who live and breathe our destruction will have thought of it long ago.
Discussing possible ways for terrorists to attack us simply allows us to better prepare, don't you agree?
Kind of like Tommy Thompson wondering out loud "I cannot understand why the terrorists have not attacked our food supply, because it is so easy to do,".
You don't flaunt weakness to the enemy, nor give them ideas.