My comments were limited to the criminal legal aspects of this. There are about a million instances where something might justify serious concern by a private party, but where arrest and prosecution would be unmerited or unconstitutional. As others have said, you can see examples by watching the reality show on this theme. An easy example where such an arrest would be unconstitutional but where a diversion might be justified would be where someone was discussing something deeply disturbing to those around them.

Again, some people seem to live in a world where the police powers in this country far exceed those permitted by the Constitution. Maybe that's because the police often ignore the limits on their power -- I don't know. Cops certainly take advantage of this knowledge gap by, for example, asking questions that folks are under no obligation to answer; you don't have to get through more than fifteen minutes of a Criminal Law class to understand what a shockingly effective tool that is. Anyway, short story is: cops are incredibly limited in what they can do, and it makes no sense to make anything out of their failure to arrest someone.