I can understand that ... but only to a degree.
Allow me to share my point of view. I am visually impaired, so I can never, and will never, be able to see if people near me are taking photos. In fact, I have accidentially photobombed legitimate PR shoots by just blindly and blisfully unaware walking straight through the shot xD.
If I sit in a car and we drive by a speedometer, can I be sure it isn't taking a picture of me? When I sit in a train and people outside on the platform take a group photo, I might be in that by sheer chance. While I am at a booth at an anime or game convention, someone might be taking press photos - and I would be non the wiser it happened. Either because I literally didn't see it, or because it was taken in stealth on purpose, for some reason.
If you are in public, and I really do mean public, unless you scan your environment like every second, you will never know who or what is or is not taking a photo of you - and unless you become paranoid in a certain way and ask everyone around you to lower their phones, you simply can't cover every circumstance.
Yes, it definitively sucks to have your picture taken without consent - lawfully or not. Yes, it is good ettiquete to not do that, not just in protests, but in general - but not everyone always thinks of this in a perfect fashion; humans aren't perfect after all :).
In these times, where surveiliance becomes more and more of a norm, masking your face is actually the best thing you can do. Doesn't matter if it's a stereotypical Guy Fawkes mask or one of those thin silicone masks to alter your facial features - it will become more important over the years. So if you don't want your picture taken in public, then make it harder to do so. Because you can never truely and fully rule it out. Maybe someone is wearing a prototype gadget as a pin on their suit that happens to have a camera and you never identified it as such? Just saying.
Now, while I understand the desire to stay "anonymous" and not feed "DA BIG CORPOS" with more data... I also have to say: Damnit, grow a pair. Has your state not already forwarded tons of ID photos to them one way or another? Have they not bought data from these firms at some point? I am 100% certain that my face is in multiple databases - not because I am particularily careless (I had posted many photos of myself when I was younger, so that opsec-ship sailed looooong ago xD) but because data exchange between corps and govts is a given now; even slow and sloppy Germany, I am quite sure.
It sucks, it really does. But what are you going to do about it? Punch in every camera and destroy each phone that possibly has caught a glimpse of your face - both from regular people and state owned cams? I mean, you could - it's an option... but - should you?