Imagine every person in a public square has a police officer following closely behind them with a microphone in one hand a video camera in the other. And we're not even touching on the 3-letter-agency relationships with tech companies which almost assuredly gives them access, even to 'private' profiles.
Innocent people should not be surveilled ruthlessly on the off chance that every now and again we catch one evil person. In my mind, it's like the TSA invading everyone's privacy without ever catching a single terrorist. It's a waste of resources, on top of being a disgusting behavior.
The difference is that in a physical public square, you have a built-in expectation of ephemerality. Everyone expects that their behavior in some random physical space is not going to persist forever. Twitter, on the other hand, is explicitly build with the expectation of what you tweet persisting forever.
On the other hand, there are tons of cameras in public spaces too. So, even though people have had a built-in expectation of ephemerality, that's already been violated for quite a while now.
Innocent people should not be surveilled ruthlessly on the off chance that every now and again we catch one evil person. In my mind, it's like the TSA invading everyone's privacy without ever catching a single terrorist. It's a waste of resources, on top of being a disgusting behavior.