I get the sense that most HN commenters are against having police surveil this kind of event in the U.S. Could someone share the reasons for this strong opposition? Personally, I can imagine valid reasons for and against conducting such surveillance. But given how many people feel otherwise, I wonder if I'm missing something.
The first obvious point is that protesting is a constitutionally protected activity, as is any political speech on Twitter, and this is interpreted extremely widely - so why are public institutions in the business of surveilling this legal, ney protected activity? But there is more to it. Courts have long recognized that state activity that can be reasonably construed to chill exercise of ones constitutional freedoms…
The first amendment is limited to protections against government interference.