I'd like to take a moment to play devils advocate here on the fanservice debate. First off, fanservice is a greatly misused word. It does not mean "tits and ass", it means servicing the fans. The most common way of doing this is T&A, but T&A is not automatically fanservice, and there can be fanservice without T&A. A lot of fans love Mako's 2 star uniform. If she gets it back, only for a minute or so, for little narrative reason, that would be pure, unadulterated, shameless service to the fans that wanted to see it again. Now, many people are arguing that what Ragyou is doing is for the purpose of getting the audience to hate her, but I don't think that's true, and it could also arguably be a way of fanservicing, though in a perplexingly negative way. Because the logic is that whatever is being done on screen when Ragyou is molesting Satsuki is for the fans sake, to make us feel a certain way. If this is the argument you are making, then maybe it can be called fanservice in a sense. However, the true test of the scenes worth is when you take the audience element out of it. What is happening then? Characterization and relationship dynamic. Those scenes reveal who Ragyou exactly is and how badly she hurt Satsuki. It shows us a different side of Satsuki, in a position that she can't just instantly overpower like she usually does. They give Satsuki all the more motivation and drive to do what she has done up until now and what she will do in the future. These scenes are not throw aways. They are vital to understanding the story, and if they serve a narrative purpose, they cannot be called fanservice, because it's not about the fans at that point, but whats happening to the characters.
That said...The fact is that these scenes are erotic. The shots linger on Satsuki's body longer and in more inappropriate places than they need to. This, I feel, is where the audience element should come into analysis, but not in a fanservicy way. It makes the audience feel disgusted, but not just with the character, but with themselves. Rape victims sometimes say that they feel arousal during their rape, as a pure physical reaction to the stimulation, which produces great shame on their part, as if they have somehow unwittingly become a willing participant due to that. The people criticising these scenes as fanservice seem to be saying that because so many Japanese anime shows have girls unwillingly getting nude for the audience as a means of arousal (including this show, at various points), they seem to be convinced these scenes are meant to evoke the same arousal without shame. The obvious tone of disapproval that the show generally evokes at these scenes suggests to me otherwise. What Ragyou is doing is obviously wrong and I don't think I've ever seen such visceral hatred in satsuki as we saw her when she stabbed her In the back. But the show isn't going to skim on the perversion here when it indulges the audience in so many other places. Tbh, the message seems to be saying to me "Look, T&A can be good fun and all, but we have to be mindful about how we do it, because it can be really fucked up as well." The only contradiction is that, especially early on in the show, there were lots of scene that basically had Ryuko being an unwilling participant in sexualizing situations. Not even fanservice, but like how Sengetsu forced himself on Ryuko the first time he got a drop of her blood. We never saw any T&A there, but he did literally force himself on her all the same, and that was played for comedy more than anything.
So while I think, if the message here is that 'fanserivce without the will of the participant is wrong', then it's not unthinkable why someone would come to the conclusion that the Ragyou scenes are trying to play to the audience, but only because of the shows earlier inconsistant tone with such a thing, rather than a problem with the scenes themselves, which do much more than mere fanservice does.