Maybe this is true in some places. In big cities in Europe and the Americas this is definitely the case. It's done by law enforcement, commercial retail, and private security. It's more or less trivial nowadays to buy a cheap IP camera and collect an database of faces across your camera network.
My guess is that there's more of this going on, but I'm only listing stuff I have personal knowledge of.
The anonymity we're talking about here is WRT the latter.
With that in mind, my point is that it's a social problem that people have to worry about death threats for expressing political opinions. It's not solved by people becoming anonymous at scale to offer up their opinions. In fact, this adds to the problem, in that anonymity tends to lead to increasingly offensive forms of expression (absent the social governor that is present IRL). Anonymity changes the motivation for engaging and removes the constraints that have social value.
It also makes it easy for bad actors to do their work.
Put simply, if people don't feel comfortable offering an opinion in person, then maybe it's not a good thing to give them an opportunity to offer it anonymously at-scale.
>Crazy shit is very culturally and contextually dependent
No. I'm speaking WRT the context of our discussion. That is, saying things anonymously online that one would not say in-person for understood social (or legal) reasons. e.g. threatening people, being overtly snarky, trolling, etc.
The internet flips this on its head because pseudonymous handles can be linked to reams of online activity that's retained effectively forever but can't be connected to a specific person. This is why "doxxing" is such a big deal online.
If online activity was like IRL activity and ephemeral, I might agree with you. But the internet never forgets.
Edit: By the way, this is not universally defined:
> say crazy shit
"Crazy shit" is very culturally and contextually dependent. If I condemn China's treatment of Uyghurs, that's fine in North America but considered "crazy shit" and can land you in jail in China. That's an extreme example, but there are plenty of other more banal differences in culture and what's acceptable globally.