The previous situations where the 4th amendment protections were subverted or revoked, or habeas corpus was revoked - all of them potentially threatened our existence (Revolutionary War, Civil War, 1st and 2nd World War - and even the Cold War). Neither the Iraq war or the war on terror is one of existence. We are fighting wholly inferior opponents with wholly inferior technology. If the war turns badly, we can annihilate our opponent thousands of times over. Even if they succeed in a major (nuclear, biological, chemical) terror attack, it will still very likely be a small scale event. You can be certain the retaliation will instead measure on the Richter scale.
I disagree with Benjamin Franklin's above quote. It should read:
"... those who desire total security at the expense of some liberty, deserve neither."
It's a sensible thing to give up the right to be individually free to build nuclear weapons or superviruses: the resulting insecurity from allowing lots of these things can result in a total loss of everything - security, liberty, and life. It is not a sensible thing to give up private communication and search and seizure because of (relatively) cheap, regional war halfway across the glove.
"If it ain't broke, don't fix it." - Bert Lantz