Social justice ideologues are not only obsessed with categorizing people into different groups based on how much they think those people are being "oppressed", and giving more or less rights and privileges to those people based on how high on this hierarchy they are (sometimes even without asking any of said people if they want that!), as well as infecting and enforcing their ideology on all aspects of society, from the highest echelons of government down to individual people's lives, but they are also obsessed with infecting works of fiction with their ideology.
Not content with simply creating new original works of fiction that conform to their standards, they want to change existing, long-established works in that manner. They want to take well-known and loved fictional characters, and change them. Either the character himself (and it's most often a he) is to be changed in some manner (such as suddenly turning out to be homosexual, out of nowhere), or the character is to be replaced by a new person who is much higher on the social justice oppression stack (such as replacing a well-established white male heterosexual character with a lesbian black female one).
Sometimes the authors of the works of fiction themselves do these changes, rather than it being demanded by SJW activists. J. K. Rowling, the author of the Harry Potter books, is perhaps one of the most well-known examples (alongside Marvel Comics).
It is quite clear that Rowling has only recently swallowed the blue pill, so to speak. (I'm sure that she might have always classified herself as a feminist, if asked, but I doubt that in the more distant past she was an actual social justice warrior per se. Just a regular rational person, rather than an ideologue.)
At one point, quite recently, she just decided that one of the major characters in the books, Albus Dumbledore, is a homosexual, and has always been. It's quite clear that she did not have this in mind at all when she wrote the majority of the earlier books. There are exactly zero hints of anything like this at all in any of the books. I highly, highly doubt she had anything like that in mind when she wrote the books. It's only an afterthought that she artificially inserted into the canon, simply because she could get away with it.
When a theater play adaptation of her books was planned, and it was planned for one of the main cast, Hermione Granger, to be black, she said pretty much "yeah, why not. She's black." Once again it's quite clear that she had never before thought of her as black. In the books she is an archetypal middle-to-upper class archetypically British young girl, with zero hints of something atypical about her, such as being black. Moreover, book covers depicting her, every single one of which she had to approve, depicted her as white. Even moreover, she was a consultant in the Harry Potter movies, where Hermione is played by Emma Watson (an upper-class archetypically British young white girl), and she had absolutely no problem with the casting. It's quite clear that Rowling always thought of Hermione as a white person, up until that theater play. But now Hermione is black, because reasons.
But, of course, social justice warriors are never, and will never be happy about anything. No matter how much things are changed, social justice warriors will always keep complaining and demanding more. There is no pleasing them.
This is biting back even Rowling. In the upcoming Fantastic Beasts sequel (the original Fantastic Beasts being a prequel to the Harry Potter books, depicting a younger Dumbledore) there are artificially inserted hints of Dumbledore's homosexuality. And that's a problem to social justice warriors. She's getting flak from them because the hints are too subtle, apparently. They are not blatant in-your-face "I'm a homosexual now!" enough.
Kudos, I suppose, for Rowling to at least try to keep the franchise within even a modicum of taste and quality, rather then outright converting it into a pure social justice propaganda machine. But now she's being attacked by her own side because of it.
I hope she learns a lesson. Although, I fear, if she learns anything, it will be the wrong lesson (as in, she might start degrading the quality of her work in order to try to please the unpleasable and eternally offended, which is an impossible task.)