Terrorists attacks cost more than lives. The direct costs of 9/11 were between $40 to $100 billion (http://en.wikipedia.org/wiki/Economic_effects_arising_from_t...). The direct costs of another terrorist attack targeting something like nuclear power could cost $700 billion or more (http://money.cnn.com/2011/03/25/news/economy/nuclear_acciden...). None of these estimates take into account indirect costs, which are potentially even larger. Preventing terrorist attacks is about saving lives, but it's also about stopping events that could wipe out a quarter of our revenue for the year. Massive economic damage can cause a lot of pain and suffering.
When analyzing risk, it's important to estimate costs as accurately as you can. Unfortunately Sam missed the boat on this one.
The overreaction to terrorism isn't a direct cost and its not part of the numbers I cited. Direct costs are insurance losses, medical care for victims, relief to widowers/widows, lost wages, etc. Those costs make up the numbers in my previous comment, which alone justify spending money on preventing terrorism. Indirect costs would be what your talking about and include things like unnecessary wars, wasteful spending on defense, currency/stock market devaluation, etc. Indirect costs are in the trillions but are harder to prove and reason about, which is why I omitted them.
I think Sam's getting at something important but it would be best to first start with estimating the costs as accurately as possible. As it stands Sam's estimates to the cost of terrorism are off by several orders of magnitude, so you can understand why I pointed that out.
When analyzing risk, it's important to estimate costs as accurately as you can. Unfortunately Sam missed the boat on this one.