In my reading, I happened upon this quote:

Take simply the attack...on the Western world, and you see how the freedoms for which America stands are tremendously narrowed down in defense of these freedoms.

However, that particular quote did not come from a Libertarian and was not about the present response to terrorism.  It is excerpted from a 1967 posthumous publication of earlier lectures from theologian Paul Tillich, in his book A History of Christian Thought (p.211, Simon and Schuster); and the exerpted words are of Communism.  He was using it as an example to explain similar events in sixteenth century Europe.  It is a natural response to a threat against freedom that freedom is curtailed for the protection of that freedom:  travel restrictions, monitoring of purchases of potentially dangerous products, and surveillance or restrictions on members of suspect groups whether suspected rationally (radical Viet Nam protestors in the 1960s) or irrationally (Japanese Americans during World War II).  As long as the threat remains viable, the impositions seem justifiable.  Once the threat evaporates, we all breathe a bit easier and our freedoms are restored.

There are, however, two caveats.

The first caveat is that it is not always simple to know when the threat ends; sometimes from within it appears that it will never end.  No one expected that the election of Ronald Reagan as President would bring the end of the Cold War, the downfall of the Soviet Union and the corresponding end to the Balance of Terror expressed in the MAD policy, Mutually Assured Destruction.  Even when the Berlin Wall fell, it was a while before we knew it was over, and even a bit longer as we wondered whether Soviet nuclear armaments would be used by radical socialist groups.  Today the death of Osama Bin Laden is a milestone, but not the end of the battle; but we are not certain what would end the battle, and answers which seem obvious to some seem ludicrous to others.  One rarely sees the light at the end of the tunnel until abruptly emerging from the darkness.

The second caveat is that the fear mongers are right in this:  life never really returns to normal.  Some vestiges of our heightened security, and therefore some impingement on our freedoms, will remain for many years.  Facing the threat of World War I, the United States passed the Selective Service Act of 1917, and from that day to this all young males (the age has varied) have been required to register with the government against the possibility that they might be needed--forced to serve in the military in an emergency.  That is a reduced level of freedom from what existed before that.  Airport boarding checks began because of hijackings and bombings, and the potential for such acts means that they will long remain part of the air travel experience, even if restrictions loosen again.  The question to be addressed, ultimately, is what impingements on our freedom will we accept as reasonable safety requirements--such as the requirement that passive restraint safety systems be included in all new automobiles, whether you wish to pay for them or not.  It puts us in the place of making the decisions, once the threat abates, as to how much freedom we will sacrifice for what level of safety.  That is a legitimate debate, and one that begins now while we still have the perspective of what the crisis is costing us compared to how it was a decade ago.  As time progresses, fewer of us will remember what the earlier freedoms were like, and it will be more difficult to discuss what restrictions on our freedom are reasonable.  Thus both voices must be heard--the one calling for the preservation of our safety and the one calling for the restoration of our freedoms--as we seek to find the new balance for the years ahead.