1. It's internalized misogyny
"Internalized misogyny" is a phrase that describes what happens when you live in a patriarchal society as a woman and you embrace the more oppressive elements of the patriarchy into your mindset without questioning why those elements are problematic. It's when a woman embraces a male - dominated point of view towards other women that often involves critizing women for being too feminine, or for not being feminine enough, depending on how a man would view their worth. It's women pitting themselves against other women for the attention of men.
Ana does this all over the place against any woman who is the slightest bit confident in their sexual expression and/or who pose as a "competitor" to her for Christian's attention.
50 Shades is riddled with clichés, but what's so sad about "girls vs girls for boys" is that it's so pervasive and normalized that people embrace it without question. A woman writing about a woman who shits on all the women around her for the desperate attention of one man isn't empowering, it's pathetic and sad.
2. It romanticizes abuse
I saw a pic (or maybe it was a text post, I can't remember) making rounds on the Internet saying something like "If you want to get a woman, act like Christian Grey".
Fellas? Let me tell you something right now: if you actually behave like Christian Grey, I'm calling the fucking cops.
We spend so much time dealing with these "mysterious bad guy" clichés that we never bother to question them, even though we really, really should. It's partially why fighting domestic violence is still incredibly difficult at times, and it's why things that romanticize a guy treating a girl like shit need to be called out and criticized loudly and often.
3. It perpetuates harmful stereotypes about BDSM
Some 50 Shades of Grey fans argue that Ana and Christian's relationship isn't abuse, it's just how a BDSM relationship works...
As we get closer to the release of the god awful movie based on the god awful Twilight fan fiction, and the popularity of the story will undoubtedly swell, there are plenty of people, including the author herself, who will be more than happy to sweep the obviously problematic issues with the book under the rug for the sake of enjoying a stupid fantasy.
Don't let them. We deserve better than this.