Idk, if a suicide bomber blows himself up in the middle of a city block should the police be allowed to forever thereafter perform an invasive frisk of your person or put you through a scanner before you're allowed to walk down the street? Hell, it's just that right to be secure in your persons, houses, papers, and effects and someone thought it essential enough to stick in an amendment.
I'm not saying that there can't be any level of security at an airport, but there has to be a balance that is proportionate to the risk. There are thousands of flights a day that come and go through our airports, and how many incidents were there before these scanners were installed? Some people live in perpetual fear and would push us toward a police state in order to try and alleviate their fears.