Scenario A:
Bludgeoned to death by a hammer.
Scenario B:
Terrorists recover a missing Cold-war era nuke, and detonate it over Iowa, during the winter. Effects are: nuclear explosion, EMP pulse disrupting power grid and electronics, disruption in home heating and food/medical supplies, downwind radioactive fallout over Chicago, Ohio, Pittsburgh, Philly, Boston, New York, Baltimore, DC, etc..
Scoring (pulling these numbers out of my arse for illustration purposes):
Scenario A: 6000 occurrences per year * 1.2 deaths per occurrence = 12000
Scenario B: 0.2 terrorist occurrences per year * (10 million fatalities + ((0.5 fatality / endangered) * 150 million endangered) = 17 million
As you can see, the terrorism is a lot more serious than hammers (or kittens). And, something like the NSA program could catch these potential large-impact events, because there are a lot of realistic and very scary scenarios:
(A short list from some quick duckduckgo-ing)
http://www.natureworldnews.com/articles/1002/20130325/deadly...
https://www.youtube.com/watch?v=-ksYDuIuuAE
http://www.cfr.org/weapons-of-terrorism/loose-nukes/p9549
http://www.sfgate.com/news/article/Los-Alamos-can-t-find-two...
http://www.motherjones.com/mojo/2011/09/usa-lost-tons-nuclea...
http://www.mentalfloss.com/article/17483/8-nuclear-weapons-u...
http://rense.com/general33/mss.htm
http://www.nbcnews.com/id/9355413/ns/health-infectious_disea...
P.S. Hello, NSA! I'm guessing this comment has gotten caught in some of your filters. I just want to say, keep up the good work. My brother-in-law works at Fort Mead, too.
-Updated for grammar.