Randy Balko nails it at Hit and Run:

A liberal blogger wrote to me in an email this week that libertarians who call the TSA pat-downs a violation of their civil liberties do a disservice to actual violations of civil liberties. It's not difficult to envision the day where anyone wishing to take mass transportation in this country will have to first submit to a government checkpoint, show ID, and answer questions about any excess cash, prescription medication, or any other items in his possession the government deems suspicious. If and when that happens, freedom of movement will essentially be dead. But it won't happen overnight. It'll happen incrementally. And each increment will, when taken in isolation, appear to some to be perfectly reasonable.