Random acts of violence will never be 100 percent prevented, but terrorism can be checked by constant vigilance, diplomacy and, yes, sometimes by the use of force. Vigilance at home and abroad helps to prevent acts of terror before they occur, diplomacy helps to defray the hatred that spawns terror in the first place and military force helps to wipe out terrorists when they are identified and to destroy the infrastructure that supports them. It also sends to message that we are not just going to sit by and take it.
Terrorists thrive in a political environment in which the government passively supports them by turning the other way to their activities. A previous letter written seems to think that just because terrorists are "willing to die for a cause, then that cause is going to be very hard to stop" and that we should just turn the other way and let them do as they will.