I don't think it's immoral and my feeling is that if people don't want to be photographed, they should stop reflecting photons. Photons are free. Nobody owns them, that would be a very strange form of ownership... I can arrange molecules that absorb light on a page and make a likeness of a person without them noticing, I just need a sketch pad, pencil and a little subtlety. Is that wrong? What if I can draw in a photorealistic style? Why would photography be different?
But then I think, well, what about the intent of the photographer? Does it matter what the usage is? I think in that case it does. Say, if you were photographing people to watch their movements and find out where they live...so that makes the photography part of criminal intent. But that's very little of photography and very hard to judge.
I think that German law is ridiculously excessive, not least of which because it gives special privileges to "journalists" who have some kind of right that non-journalists don't. As an independent journalist, that really burns me and I think it's wrong. What makes those two shots presented by the OP not journalism? They aren't published by anybody? Well, they are, by the photographer. They don't show things of journalistic interest? Why not? Don't they speak to the human condition? Are they not documentary, and what makes that not journalism. The disturbing conclusion is that they are not journalism because our OP is not professional, ie, not paid by someone who can judge his work legitimate and worthy of being shown. I have problems with this!
Lots of people are photographed 1000s of times a day by security cameras and they don't complain. Is that wrong? Lots of people would say no, its not, I guess because it's some "official" organization doing the photographing and anyway, only the guilty need fear, right? In fact I do find that wrong, not so much for what it's doing (essentially the same thing as a hip-shooting street photographer) but for the intent, which is to spy, pry and control.
I think there are lots of shots that can't be gotten by direct intervention in a scene. Some of those are on this thread, and there is a literalism and spontaneity to those shots that I really like.
Morality aside, I don't do much shooting like this. I try to use my photography to interact with people and the world around me, to push myself to be more outgoing. I use journalism the same way. In general I think consent is a nice thing to do and it gives the photographer a chance to interact with someone they don't know. I don't think it's a moral necessity but a nicety.
Last night I was shooting a restaurant and one of the servers asked not to be photographed. Pretty much totally against what I was trying to do, which was to document the restaurant in action. But I respected her wishes, not because I thought she was in her rights (I didn't), but because she asked and I could get away with it and still tell the story I needed to tell. I felt good about that, and so did she. She was the nicest to me during the shoot, too. So there is a consideration I have for the other person...will my photography (or restraint of it) humanize or dehumanize that person? If I know it's the latter, then that reflects on my intent.
I'd like the security agencies to ask the same thing.