There's a reason why some variation of the quote "laws are like sausages - it's better to not see them get made" has endured: we all understand that there are certain things that look better the less you know about them. If you show all the steps that are involved in making something complicated you're probably going to strip the magic out of that object. In fact, you might even turn it into something horrifying.
Last night I watched American Mary, which is about a young woman who drops out of medical school due to some unfortunate circumstances and ends up as a back alley surgeon who does illegal body modifications on people that don't want to look human anymore. She operates on a lot of willing participants (who seem mostly happy with her work) and on a few unwilling participants (who are very unhappy with her work) but I was equally uncomfortable watching her operate on both types of patients. Body horror has always been the most disturbing horror genre to me; I'm less worried about being murdered than I am about being reduced to a pile of meat, and as a surgeon Mary has treat both her patients and her victims like they were slabs of beef.
After I was done with the movie I started thinking about the surgeries she performed that people actually get in real life - adding horns to their heads, removing their nipples, splitting their tongues - and what made me so uncomfortable about them. Eventually I started to think about the Little Mermaid, and how frightnening that story would be if it fixated on how her fins turned into legs; if the sea-witch had bonesaws instead of magic potions it would immediately go from a children's story to a nightmare. That's when I started to key in on what makes those voluntary surgeries seem so crazy to me: it's not the desire to change, it's wanting to change so badly that you're willing to go through intense pain.
If we lived in a world like the one the Little Mermaid lives in and you could take a magic potion and become something else it wouldn't strike me as insane to drink that potion. Ill advised, perhaps, as deals with the devil often are, but not crazy. But in the absence of magic there's only medicine, and medicine is imperfect and painful. The people Mary works on go through torments in an effort to evolve but to no avail: they will always be people, but now they've become people who have been ripped apart.
What makes me uncomfortable about American Mary, then, is that it's about how the sausage gets made in a way that a lot of movies generally aren't. And I'm not just talking about fairy tale movies - though, yes, the Little Mermaid might have suffered terribly as she was transforming into a human, but that part is so brief it's almost an ellipses in the broader romance - I'm talking about movies in general, since violence in movies often has negligible consequences. People who get hurt immediately die and then disappear from the screen. That's not what's happening in American Mary: we see her patients being marked up and then cut into, and then when they are walking around it looks obvious that they've been worked upon. There's no ellipses here to brush past the unpleasant implications of what she's done.
I have to say that at the end of the day I would rather not know how the sausage is made. I don't find it pleasant to think about; I prefer magic to reality on some level, because magic is fun and reality is full of damaged meat. But my discomfort with American Mary is a feature, not a bug; it got the desired reaction from me, and I have to give it credit for that.