It has taken me a while, but this nails it:

Security measures combat a very different sort of risk: a risk stemming from another person. People are intelligent, and they can adapt to new security measures in ways nature cannot. An earthquake isn't able to figure out how to topple structures constructed under some new and safer building code, and an automobile won't invent a new form of accident that undermines medical advances that have made existing accidents more survivable. But a terrorist will change his tactics and targets in response to new security measures. An otherwise innocent person will change his behavior in response to a police force that compels compliance at the threat of a Taser. We will all change, living in a surveillance state.