Over long time, and especially since 2001 many people are very concerned about terrorism - and much money is spent and lots of silly procedures have been invented to protect us.
This very good article puts the risk of terrorism into perspective - and the risk of falling victim to a terrorist attack are really negligible compared to many other risks which we simply accept as fact of life (like car accidents - in the US the probability is about 500 times higher to die in car accidents as compared to terrorism; homicide risk is 175 times as high as terrorism).
So actually the relative spending is unreasonable and actually irresponsible.
Of course, this is not only true for the US.
From the article:
"Compared with dying at the hands of a terrorist, Americans are twice as likely to perish in a natural disaster and nearly a thousand times more likely to be killed in some type of accident."
"As a hazard to human life in the United States, or in virtually any country outside of a war zone, terrorism under present conditions presents a threat that is hardly existential. Applying widely accepted criteria established after much research by regulators and decision-makers, the risks from terrorism are low enough to be deemed acceptable. Overall, vastly more lives could have been saved if counterterrorism funds had instead been spent on combating hazards that present unacceptable risks."