> Just remind them, public photography is not a crime, and that there is no right to privacy in the public sphere
That is completely incorrect in Germany. If the person photographed is in any way the center of the picture and not just one of 20 people in the background, you have to ask for permission first.
If the person is in public, and they are incidental to the subject of the photo, permission is not required.
If you are taking a picture of a stranger, of course you have to ask their permission.
These two things are not the same.