Yeah i get your point. But if people want to take pictures of their live (with foreigners without asking them), then they can also do it now. But most of them are not doing it.

A few friends of mine have BeReal. and from time to time i watched reals of other people (who i also know personally). What i like is that you get a good impression what they are doing even though you do not see them often.

But yeah sometimes there might be people on it you did not agree to publish this foto.

On a centralized platform (with open source technology) there is probably less guarantee that the pictures are really deleted (after a few days) but maybe you should trust the sw developer/hoster.