Originally Posted by
Altima of the Gates
Honestly, its pretty much because people have a filter that tries to say life can't be that bad, so if you go over a certain threshold the filter goes off. I echo the sentiments that this is a universe where shit is this bad, all the time. Children being used to experiment with magical disease, a guy who knocks up a one year old homunculus he basically molded into his wife and having a half breed homunculus daughter who was modified in the womb and then experimented on outside of it, orphans rotting in a basement alive, the list goes on. And I also echo the statement that there are far more extreme scenarios that people don't really blink an eye at and just read the story.
They distinctly show that she is a magical experiment, and that the scenes that show the familiars making her body respond with stimulation also say that she is being asphyxiated. Its uncomfortable because if someone was experimenting on the body of someone you knew like that, it wouldn't be pretty or nice. It would uncomfortable and vile, but that would be the point about why Sakura retreats from people, because its hard to feel proud of yourself when you are that degraded(kinda hot take, but its why Rin is terribad actually bringing her up out of the depression, trying to force her to feel dignified but not really grasping why its hard for her to feel proud, to have confidence, Shirou kinda sorta points it out but his admiration of Rin stops him from really hammering that point home for her).
That alienation would suck to live with, and its a part of her character that you have to see in order to get the whys and how's of her thought processes.
That said, Nasu does say that her story is sexual in nature, but its doesn't mean what's depicted isn't harmful. Sadists likely could get off to that, but people can get off to anything, so what's the point?