For one example take the paparrazi. While many people consider what the paparrazi does to be an invasion of privacy, it is not legally defined as such, and is therefore legal. Now imagine if there was a paparrazi on every single street corner, wirelessly connected so that any time any person of interest passes through any intersection, a photo of them with a timestamp is uploaded to the internet instantaneously. Would that be an invasion of privacy? Now what if these same paparrazos on every street corner just so happened to not be real people, but cameras covering every angle of the intersection? How quickly what "isn't an invasion of privacy because you're in public" becomes a terrifying scenario.