Article in Slate about missile defense and how it doesn't work.

I had a professor in college who was adamantly against SDI or Star Wars or missile defense or whatever today's name is. He wasn't a technical guy, he was a poli-sci prof. Basically, his argument went, we create an instability in MAD (or its modern day equivalent) by having a system that can stop the missiles that other countries launch at us. It makes countries that have the ability to destroy feel that they aren't safe as we will have a first strike advantage: we can launch our weapons at them, and even if they launch something back, we can stop it with our LASERs (or whatever) in the air. The opposing country becomes very frightened at the prospect and does something stupid in order to make use feel the fear they feel. We may say to the world that such a system is just for our own protection, but other countries see it differently--and we need to recognize that.

I agree with this line of reasoning, and also think that there is no way missile defense will protect us against terrorists. Terrorists aren't going to invest millions in a missile system to launch bombs from a distance, not while they have people willing to be suicide bombers.