I think the line is usually defined as you have no expectation of privacy in public, at least that was the justification for the CCTV in the UK (and other English Common Law jurisdictions).

I don't think you should destroy anything, there are other ways to go about expressing disdain that don't lead to laws being broken.

It might be cultural but I wouldn't be freaked out by the petrol station camera. If they are scanning faces, then it is only to locate the head of a moving subject, there is no facial DB consisting of every citizen for them to draw from and if they are scanning license plates then there is obviously enough people pulling a runner to justify investment in newer, more expensive tools for an old problem, sounds fair enough to me. Isn't that the point of having a license number? A publicly visible identification number for a specific vehicle?

For me there is a difference in picking information up (in an automatic fashion) that people throw away willy nilly and getting information that is protected.