This is an important part of the story. Public decency laws, and nude beaches as an official exception to them, are not there to protect the nude people, they're there to protect the prude from the nude.
The sad truth is, however, that while being nude at a nude beach is OK, having a picture taken of you and distributed outside that context is not OK. For one thing, it violates my feeling of privacy more than a picture of me walking in the park (I guess there is still a remnant of prudishness there), but it can also damage my reputation and social standing among people who dislike nudity. Thus, it makes perfect sense to be stricter about taking and distributing pictures from nude beaches, just like there is a distinction between taking a picture of me in my front garden (maybe ok?), sunbathing in my back garden (less ok), watching television in my living room (bad) and having fun in the bedroom or bathroom (really bad).
(Note also that most people don't go to nude beaches because they're exhibitionist: they go there because it is much nicer to sunbathe and swim without swimming gear. If you've never swum naked, you should really try it one day, it's a world of difference)