Me and my fellow white people call each other "white trash." That doesn't make it acceptable for an out-group to refer to novels by white people as "white trash books." It would, in fact, be a slur to do that. (I'm sure you've by now drawn the connection to other slurs used by in- and out-groups.)
Again, "fanzines" were and ARE called that by the people (the fans!) who make them. Fanzines were put together by people who had the time and disposable income to assemble a physical magazine for fun, not profit. There was no pejorative meaning associated; it's like calling people who knit knitters.