So what you are saying is, we need microphones on every street corner running natural language processing and speech recognition software to identify and record any threats someone may make?
That's different from the federal government having power to eavesdrop on all street corners at all times. The fears over these powers aren't based in a desire to keep the government in the dark, they're a reaction to the massive scope, and the notion that everyone is suspicious all the time.
It's much more than the people around you taking it upon themselves to report your threats.