When the Wrestler came out, as a wrestling fan, I was pretty aware of what the reception was in the wrestling world. I don't think I read a single negative review from the people who make up that fringe interest. One former star noted it was in no way as bleak, but noted how accurate the film was when it came to representing how much physical pain actually goes into it, the way the matches were laid out, the "in ring" performance given, etc. Granted, ballet is a more focused art form, but the top names in wrestling will also spend years getting to where they are (e.g. Mick Foley, who has been getting a lot of media attention via the Daily Show. He knows the business. It is his life. And he respected the Wrestler as a film, and the portrayal Rourke gave, to my recollection).
Some people just want to complain that their fringe interest is not being well represented.
edit: I just read that Vince McMahon, the owner of the WWE, hated the film. But that guy is a douche bag and someone who half the time makes sure his performers are set for life after their careers are done and the other half of the time pretty much sends them out to the trash and forgets them, so who gives a shit what he thinks.