Once upon a time, FBI tracked everyone who read certain books from the library. This was illegal and against the spirit of the fourth amendment to the Constitution of the United States (this was before the PATRIOT act and countless SCOTUS carve-outs since). But they did it anyways, and invented parallel constructions to how they detected the guys they wanted.

For now, because you add on a computer or on the internet makes it a new instance, it's still legal for them to do dragnet surveillance.

But then the people are the enemy of the justice system and government institutions, which should tell you something.