The problem is, what is legal today might not be tomorrow. Especially depending on the regime in power at the time.
Mass surveillance can implicate someone in a crime if later on some regime decides that what they did or where they went is now a crime when it wasn't before.
Remember the push back against Apple's proposed client side scanning of photos to look for CSAM? What happens when the hash database starts including things like political memes, or other types of photos. What used to be legal is now not, and you get screwed because of the surveillance state.
Absolutely no data should be available without a warrant and subpoena, full stop. Warrants issued by a court, not a secret national security letter with a gag order either. Warrants only issued with true probable cause, not "acting suspicious."