alt Hacker NewsOP's contention is that private citizens don't have access to a network of cameras to look for license plates and therefore it isn't "plain view", but I don't see how that's different than law enforcement being able to muster the entire nation's cops to look for a suspect.
Because it is not about some principle that cares about the nature of the action, the principles are related to the civil liberties at risk, and whether or not certain powers jeopardize them.
The level of observability and risk involved in using the entire nation’s police resources is extremely high, whoever asks for that much resources will have to account for what they are doing and many of the details of the event are likely to be scrutinized by many parties, media, other departments, etc. It is unlikely to be wielded to abuse or strip civil liberties or to harass people, as we’ve seen ALPR’s be used