Even for people who don't take the 'anything for safety!!' line, the harm of radiation is invisible, speculative, and in the future, whereas the harm of the humiliating patdown is palpable, certain, and immediate. There's a lot of research on cognitive biases that suggests that people tend to prefer to expose themselves to objectively unreasonable risks (that is, risks of greater harm, even discounted for the low probability of occurrence) in preference to the choosing of certain, smaller harms.

I respect whatever choices people make, as long as they are actively making a choice. That's why I talk to my friends and colleagues about why I opt out. I believe that knowing more about the facts makes for more informed decidion-making; and it's definitely persuaded some of my friends and co-workers to opt out.