Did you transpose false negative and false positive in your statement about airport security? I think airport security would much rather have false positive (i.e. This guy has something suspicious, let's do further checks, oh, turns out it was nothing) vs. False negatives (i.e. This guy is clean, oh, turns out he wasn't and blew up a plane).
No, that's correct. The issue is that the overwhelming majority of people aren't terrorists. So even though it's worse to let a terrorist on a plane than it is to ban someone who isn't a terrorist from flying, in aggregate the harms of banning non-terrorists from flying become greater than the harms letting a few terrorists fly even when the false positive rate is very small. Bruce Schneier has a good explanation of this somewhere on his blog. (Actually, this is one of his pet issues, so there are probably dozens of blog posts about this.)
