You could refuse security screening. Then the airline can and will refuse to fly you, and in my previous life I have denied boarding to two customers who did not desire to have their bags opened in secondary screening. This is stated pretty specifically in conditions of carriage at my former employer and I'm sure at the other carriers as well.

You raise an interesting point regarding screening upon arrival. That, I am not sure. I'm all but certain that a refusal would result in at least an interview with law enforcement.

As far as the "point of no return" at the checkpoint. (Keep in mind this was current as of 6 months ago) If you elect to withdraw from the screening process before it has begun, that's your business. However, if you enter the process, and alarm, they are required to contact law enforcement if you then elect to withdraw. Doesn't mean you will be arrested. Just means that they have to alert law enforcement. I'm sure someone like TSAMGR or other folks can elaborate on this.