> SSN is voluntary. USA passport application has a spot for SSN and it may be left blank or may accidentally contain rando numbers (I have done both). TSA full body scan is also voluntary, along with voluntary showing ID at their (Soviet era) checkpoints.

I had to do a quick check on this TSA scan just to confirm that an opt out was possible, seems they changed the language back in 2015 https://www.dhs.gov/sites/default/files/publications/privacy... (page 3) to make it less optional. Basically it sounds like you can say NO, but they can override your NO for whatever reason..

"TSA is updating the AIT PIA to reflect a change to the operating protocol regarding the ability of individuals to opt out of AIT screening in favor of physical screening. While passengers may generally decline AIT screening in favor of physical screening, TSA may direct mandatory AIT screening for some passengers as warranted by security considerations in order to safeguard transportation security."