They have no right for cameras in public.
I'm pretty sure they do. That comes along with the word "public". This sounds like ICE telling observers to stop filming.
Collecting the footage from thousands of cameras and turning it into a giant surveillance system to track everyone is a different matter, and that's what needs to be made illegal.
My purity test is that anyone who uses the term "purity test" unironically is either braindead or an establishment clown.