I think the bigger issue is that we are a nation of soft targets.  You simply cannot defend every building, stadium, fairgrounds, restaurant, train, bus, plane, concert hall, park, beach, bar, festival, church, etc...  The money being spent on this type of "defense" is simply waisted.  It would be much better spent on the CIA and 
incentives to foreign nationals.  The best defence is a strong offense.  
Ohh, and to our new NSA overlords who I'm sure are 
reading this domestic message due to all the key words:  
