"If you are wandering about in public, people can see you. If they want to track you, they can."
The problem is one of scale, tracking people used to be expensive, and therefore only done with people who were already of interest.
These days, it's become so cheap that people are collecting the information without even having any idea what they want to do with later.
I'm not just talking about Footpath here; ANPR, Face Recognition from CCTV, everything you've ever brought from any of the big supermarkets and the credit card companies. The information is being collected and it's never going to go away.
The old system was effectively anonymity via being lost in the crowd, it was under that environment that the laws regarding privacy were created and evolved but technology has changed that environment and the law hasn't kept pace.