Here's what happened to me the last time I went through a TSA checkpoint:
I opted out. The TSA agent made a snide remark about about me being separated from my belongings, which I'd already put on the X-ray conveyor belt [2]. Then, I was forced to wait about half an hour until an agent was free [3]. There were TSA agents standing around, not doing anything, but, those people, apparently, can't do pat downs.
When an approved agent was finally free, instead of cordially walking me over to the pat down area, he shoved and body checked me to get me to move. After the perfunctory patdown, he pointed to my luggage and said I could go get it. He then stepped in front of me as I started walking towards it and gave me one last shove, away from my luggage.
So, do I like the TSA? Of course not. I have practical and philosophical objections to their process, and perhaps 20% of the time when I opt out, I'm treated like human garbage [4]. But, most people don't have any weirdo academic objections, so they go through the regular process and everything is fine, 99% of the time. Sure, they have to to the airport half an hour earlier now, but that's a small price to pay for what they see as protection from terrorists.
[1] http://www.forbes.com/sites/tedreed/2012/08/09/surprise-gall...
[2] It's a bit like being threatened by the mafia: those are some nice things you have there. It would be such a shame if anything happened to them while you're away. This was sufficient to keep two couples, who initially decided to opt-out, from actually opting out.
[3] https://twitter.com/someben/status/274976070271377409
[4] It's like walking into a random replication of the Stanford Prison experimenter [5]. Will the guards be aggressively unpleasant? Maybe!
[5] http://www.lucifereffect.com/about_content_extensions.htm