I'm not entirely sure what the US constitution says about a reasonable expectation of privacy, but I certainly have to wonder what the authors of it would have changed, had they envisioned a society in which the government could constantly, reliably, and ubiquitously surveil its' citizens.

That is, perhaps we shouldn't have an expectation of privacy in public, but for a long time, we had a reasonable expectation of relative anonymity, at least, the average person did.