There's a saying in China, "don't use a cannon to kill mosquitoes."
The mosquito is small, so small that you don't see the threat until it sucks your blood. It hums around, annoys you, and leaves before you feel the itch. It attacks you under most unexpected circumstances. Even the biggest cannon can not solve the problem. So is terrorism.
There are several things that makes terrorism scary.
First, terrorists are creative. They are good at surprises. Fighting a hot war is bad, but being scared of unknown enemy is worse. Terror itself can cause equal damage as the real attacks.
Second, modern technology exponentially increased terror groups' destructiveness. Terrorists have easy access to many cheap and lethal tools.
Third, our civilized world is set up like a domino. We are so inter-connected that one explosion may cause a global chain reaction. We made ourselves highly vulnerable when black swans show up.
In the past, the conventional superpower can rest assured and neglect the small groups of unhappy humans. Now they can't. Through terror, the small/minority/weak groups bring themselves to the attention of the whole world. People are forced to face and deal with the questions that are long forgotten.
At the same time, the terrorist attacks also bring war into the middle of modernity, where people are too used to peace and only observe wars on CNN or hear about the rising casualty of foreign people in remote areas. Examples are 9.11 in New York and the most recent bombing in Moscow. A Chechen rebel leader said, "If Russians think that the war is happening only on television, somewhere far off in the Caucasus, and it will not touch them, then we are going to show them that this war will return to their homes".
On the other hand: if you are a marginalized group who has constantly been endangered/weakened/neglected by the giant, the one remaining thing you can do is to sting the giant with all your force.
Terrorism against civilians is absolutely evil. However, we should also remember that suicide bombing is not the top choice for anyone. People turn to terror under desperation.
Now most of the anti-terror efforts are directed toward intelligence work, regional wars and fancier full-body scanner. How to prevent desperation in the first place is the topic that is worth working on. Using the "cannon-mosquito" parable: we shouldn't build new billion-dollar cannons. Instead, let's dry up the swamps where mosquitoes grow.
It's always easier said than done. The core problem here is: can the strong put down its pride and arrogance, and try to sincerely understand, listen to and cater to the need of the weak, before all disasters happen?