So, there’s this girl. She’s tragically orphaned and richer than anyone on the planet. Every guy she meets falls in love with her, but in between torrid romances she rejects them all because she dedicated to what is Pure and Good. She has genius level intellect, Olympic-athelete level athletic ability and incredible good looks. She is consumed by terrible angst, but this only makes guys want her more. She has no superhuman abilities, yet she is more competent than her superhuman friends and defeats superhumans with ease. She has unshakably loyal friends and allies, despite the fact she treats them pretty badly. They fear and respect her, and defer to her orders. Everyone is obsessed with her, even her enemies are attracted to her. She can plan ahead for anything and she’s generally right with any conclusion she makes. People who defy her are inevitably wrong.
God, what a Mary Sue.
I just described Batman.
Wish fulfillment characters have been around since the beginning of time. The good guys tend to win, get the girl and have everything fall into place for them. It’s only when women started doing it that it became a problem.
TV Tropes on the origin of Mary Sue:
The prototypical Mary Sue is an original female character in a fanfic who obviously serves as an idealized version of the author mainly for the purpose of Wish Fulfillment.
Notice the strange emphasis on female here. TV Tropes goes on to say that is took a long time for the male counterpart “Marty Stu” to be used. “Most fanfic writers are girls” is given as the reason. So when women dominate a genre, that means people are on close watch, ready to scorn any wish fulfillment they may engage in. This term could only originate if the default was female.