A cop can follow you on the public streets legally, recording where you go, who you talk to and want you say. But imagine drones cost 5cents, would we want the cops to be able to launch a drone to follow every single person every moment they are on a public street?
No, that would be a dystopia.
Technological change means the consequence of a law changes. And so perhaps a different set of laws achieves our societal values better in light of a change.
I actually don't see that as the key element at all - Doing something that is already legal, faster, doesn't make it illegal does it?