If you've had to kill time sometime within the past couple of months, you might have, against all reason, turned on one of the political debates. What with all the recent high-profile terrorist attacks, politicians are positioning themselves to pretend to be able to solve terrorism by the same tried and true methods, which have been tried and shown to be truly worthless.
Nothing the government can or ever will do will protect you from a terrorist attack for the mere fact that the government is centralized and monolithic and terrorism is diffuse and nimble. A little thought about this should make it obvious. Put yourself in the position of a terrorist. Let's say you have the goal of causing as much havoc as possible for whatever your sense of greater glory is. You can do this easily.
You can drive your car into a crowd at a mall or park, you can go in public with a gun or knife or axe and stab people, you can release over-the-counter noxious chemicals in movie theaters or trains or whatever. You could probably still pretty easily hijack a plane with some improvised weapon.
Even if terrorism were preceded by some constant identifiable red-flag behavior, the ease and difusness of it makes it impossible for central agencies to respond to. The only real response to terrorism can be physically local security, well-equiped average Joes, general preparedness etc.
If you think about the actual government policy that would be required to prevent someone from slamming their car into a crowd of people or keeping someone from taking an axe in public and you realize for the state to prevent any kind of terrorism would require substantial and universal curtailment of things that even neoconservatives think of as being "basic freedoms." A place immune to terrorism would look substantially worse than North Korea. And even the universal surveillance we live under already has been proven apt only at prosecuting criminals after the fact.
Aside from that, people seem to have forgotten what the word "terrorism" means. Terrorists don't benefit from killing people per se, they benefit politically and socially from the terror they engender. This terror would be impossible if the media and the political class were not there to aid them and shout their actions from the rooftops. At that, because the media and the political class thrive on fear as well, they and terrorists are in a symbiotic relationship arrayed against the public.
Of course one question you might have is if terrorism is so easy, why don't more people commit it? The simple answer is probably that 99% of "extremists" of any sort are all bark and no bite. They don't want to me martyrs because they're human.