I am a conservative Republican who voted for Bush (three times -- once for governor, when I lived in Texas, and twice for President) and I have an answer for that question.
Answer: I can no longer sit and talk with my family at the airport, while they're waiting to board a flight, unless I, too, have a boarding pass. When they're going to be gone for weeks or months at a time, it used to be nice to joke and laugh with them before they got on their flight.
In a post-9/11 world I no longer can do the above.
Is that a civil liberty?
Well said my brother.