Good intentions by lawmakers often fail to achieve the desired outcomes, because “virtually all public policies alter the relationship between costs and benefits. When the benefits of an action change relative to an action’s opportunity cost, people’s actions also change. And when people change their actions, they may do so in a way that works at cross-purposes with a public policy’s noble intentions”.
As an example, after the 9/11 attacks, the Transportation Security Administration security measures raised the opportunity costs of flying, since people after that had to wait much longer in line. As a result, some shifted to automobile travel. But fatal accidents are much more likely to occur in cars than airplanes, and one estimate is that because of the TSA’s policies, “327 additional automobile deaths occurred monthly for the last quarter of 2001”
(No Free Lunch: Six Economic Lies You’ve Been Taught and Probably Believe by Caleb S. Fuller, pp. 48-52)
Of course, they haven’t stopped even one non-governmental terrorist…