Popular culture has an influence on society. As an individual you may be able to place a book down, turn a movie off and it has no influence on you, other people can and will be influenced by what they read, watch or hear.
Never make the assumption anyone else thinks the way you do or is immune from outside influences. To be honest, it sounds rather arrogant on your part and demeaning to others.
We live in a society where popular culture influences fashion, dining choices, even choices in pets.
50 Shades is part mainstream pop culture where most BDSM novels are not. For a segment of the population, that book is their only glimpse into the Dom/Sub world, and it is a staggeringly poor representation of that world.
I know erotica/BDSM writers and people who practice BDSM. They are appalled at the gross misrepresentation and abuse EL James writes about as part of a BDSM relationship. Their concerns are valid and understandable. Absolute trust is at the heart of every BDSM relationship, EL James spits on that.
Doms are upset at being portrayed as narcissist, manipulative abusers, who care nothing for their Sub. Subs are angry at being portrayed as naive, simpletons who readily and happily accept their Doms' abuse and betrayal of trust and keep coming back for more.
If she did any research on the BDSM world, it was poorly done or James disregarded what she learned. If she did none (Which by all accounts appears to be the case) she deliberately made up her version of what goes on in those relationships. Why shouldn't she be open to criticism under either circumstance?
Societally James portrayal that as long as a man is rich and good looking he can abuse a woman as he pleases and she will allow it is at the very core of rape culture. It reinforces the message women want to be raped and abused.
People are discussing the topics in the book and their anger at them. Part of that discussion is centered squarely on the author who wrote an absurd misrepresentation of a very specific world.
One of the first things most authors learn is know the subject they're writing about. It is a guarantee, that unless an author is creating the entire world their story takes place in, they are going to be subjected to critique by those in the world the author wrote about. If the author chooses to misrepresent that world they open themselves up to vocal criticism. And when the misrepresentation goes to the extent of reinforcing a large societal problem, such as in the case of FSOG, that rape victims enjoy it, that criticism will more than likely be deafening.