As I have just recently been subjected to this, I can tell ya, I am not happy about it. I not only had to go through the full body scanner, I had to be patted down also. Now if it is a one or the other (if you choose to opt out of the scanner), then why did I have to be subjected to both? I felt like I was a prisoner honestly. The only crime I was committing was trying to get to a job so I can earn a living.
News reports have shown that it is a random selection of people to be selected to go through the scanner as there are not enough scanners to go around. When you are selecting a random group to go through, you enter the reasonable suspicion/probable cause realm and to do searches under such assumptions, you need to have reasonable suspicion in order to do such a search. No one I have seen subjected to either has acted in any way to cause suspicion.
My question is, after I pay $132 to TSA to get a TWIC card after a thorough background check, will I still have to be subjected to said searches? I prove who I am with an official US passport no matter if I fly domestically or internationally.