Ohio State's John Mueller has outlined an elegant, reasonable, sensible approach to terrorism policy (pdf). Which of course is why it will get very little consideration in Washington. Mueller's premises:
1. The number of potential terrorist targets is essentially infinite.
2. The probability that any individual target will be attacked is essentially zero.
3. If one potential target happens to enjoy a degree of protection, the agile terrorist usually can readily move on to another one.
4. Most targets are "vulnerable" in that it is not very difficult to damage them, but invulnerable in that they can be rebuilt in fairly short order and at tolerable expense.
5. It is essentially impossible to make a very wide variety of potential terrorist targets invulnerable except by completely closing them down.
And his policy prescriptions:
1. Any protective policy should be compared to a "null case": do nothing, and use the money saved to rebuild and to compensate any victims.
2. Abandon any effort to imagine a terrorist target list.
3. Consider negative effects of protection measures: not only direct cost, but inconvenience, enhancement of fear, negative economic impacts, reduction of liberties.
4. Consider the opportunity costs, the tradeoffs, of protection measures.
Via Bruce Schneier.