What is with people obsession with realism? Like, in what moment the series even implied it would be a manual to BDSM?
You'll note that this was NOT at any time presented as a fantasy or SF story, thus placing it in some semblance of the real world, with the characters taking part in some semblance of real activities, albeit clearly hampered by the author's misunderstanding of how they actually work. So yes, it's implied to take place in the real world, magical aphrodisiac aside.
So? Is a fictional story. For definition the audience have come to accept breaks from reality due artistic reasons. Or are you telling me you think CSI or Law and Order are accurate representations of the way the legal system works in the US?
Not to mention, the author has chosen to take it upon herself to portray a practice which is much misunderstood and maligned thereby, so criticizing her when she gets it catastrophically wrong is absolutely fair game. No need for it to be "a manual to BDSM" to call it out on being as good at BDSM as "the ankle bone's connected to the neck bone" is an example of good anatomy.
Thing is, the BDSM is not really the focus of the story as much as a device to mold the setting and the characters according to the authors' vision. And that is something the story hasn't been concealed from the audience since the start. So expecting something more is pointless.
