The entire purpose of terrorism is to create fear in the population whether it be in the group the terrorists control or the group that the terrorists would like to control. It can be said that the terrorists in the 9/11 attacks were successful in that regard.
For the most part, we have been reacting from a position of fear. This fear has manifested as people yielding their liberty to the government in exchange for a false sense of security.
In other words, the terrorists have been able to get into our heads. This is exactly what they want. They want us to be fearful of them because that gives them influence over us.
With the recent attacks, it might be tempting to react from a stance of fear. This would be the wrong thing to do. Not only does this allow the terrorist to win, it allows the government to take even more of our liberties from us.
This does not mean that we should not do anything. What it means is that our response needs to be well regulated and appropriate. Fear should not be an option.