It's a matter of the principle - if you don't stand by the right to have freedom, someone will eventually erode it piece by piece. And The People will not care

It's a matter of the principle - if you don't stand by the right to have freedom, someone will eventually erode it piece by piece. And The People will not care because "it's just a security check at an airport". It has been shown that they offer little to no added security, but they do reveal a lot about you and it is in electronic form. If it somehow was guaranteed that this information would never leak it would be a non concern - that is however not the case (they need to preserve this information in case it is needed). It is comparable to pictures of a strip search getting leaked.