Originally Posted by ND Sol

A simple explanation might be "control" or the "perception of control."

TSORon does not have any control over my actions on this board anymore so than any other poster. As such, no control (or even perception of control) and no government actor.

At a checkpoint, the TSO requires ID, requires an administrative search and a secondary if deemed necessary. And there is the perception that they can stop you from flying. In addition, the TSO can determine that any item you have is prohibited and will not be allowed into the sterile area. So when a TSO at the checkpoint calls you an idiot for wearing a shirt with language the TSO doesn't like, the potential perceived repercussions exist. As such, you will have second thoughts about whether you will wear the shirt. That is the "chilling effect."