Observation: it is legal to listen to a conversation happening in public, and it is not typically legal to record it.
Some things that are not much of a problem at a small scale ("take a picture of a specific strange thing you see happening", "record one license plate of a specific car in relation to an incident") can become a problem at scale ("set up a video camera to constantly surveil the sidewalk and do facial recognition on it", "record every license plate that goes by and correlate your recordings with a million other people to generate a tracking map").
The problem is with pervasive surveillance, not discrete observation, and that's the spirit that laws about surveillance should attempt to uphold.
> Observation: it is legal to listen to a conversation happening in public, and it is not typically legal to record it.
That doesn't seem accurate. Do you have an example of a law that prohibits filming on public property? Isn't the legality the whole premise of what those weirdo "first amendment auditors" on YouTube do?
Depends on your local law, but in many, many places you cannot legally record a conversation you aren't a party to, even in public. In the US, in many states, it's not permitted to record a conversation you are a party to if others have not consented. There are various reasonable exceptions that permit recordings (e.g. public events, press conferences, trials, governmental meetings, recording interactions with police). "Conversation between two people happening in public" is not typically a permitted exception for recording.
Note that in this comment I'm talking about audio recording, which typically has much stricter regulations than video recording. I think the same principles should apply to video, and in some jurisdictions they do. But in my comment, I was using the laws around audio recordings vs physical eavesdropping to make an analogy about the problem of pervasive surveillance.
If I decide to take a picture of what's going on outside my house for no reason at all, should that also be allowed?
if I decide to put a camera in my living room pointed out the window and record, should that be allowed?
If I decide to run a business out of my home, does that change anything?