TSA are not law enforcement and have no authority to arrest nor detain. This is why there is always a bored actual cop sitting somewhere nearby. The cop can arrest.

You can try this yourself - get some old shoe trees with metal posts and fold one of them at 90 degrees so the scan machine flags it as a firearm. If TSA can't figure out the puzzle you made for them, they leave the bag in the tunnel, and it doesn't move until the actual police take it out and look inside. Yes, I experienced this.

Also, I opt out every time. It has been hundreds of times. No big deal.