This is straightforward: We've spent more than 5 trillion on the war against terrorism, homeland security, NSA, and other measures as a response to 9/11.
If you want to talk money and not lives, then by your citation we're spending the equivalent economical impact of a large terrorist attack every month to prevent something that is more rare than being struck with lightning from happening.
http://nationalpriorities.org/cost-of/
If you want to talk money and not lives, then by your citation we're spending the equivalent economical impact of a large terrorist attack every month to prevent something that is more rare than being struck with lightning from happening.