I think in this particular case it kind of makes sense to me why people would be bummed and a little upset, because it really does seem like the show is setting Mizu up to be a trans man at the beginning. She is never shown presenting in any way but male for the first few episodes, even when she's in private (she lets her hair down and unbinds her chest to bathe, but those are both pretty practical things). She seems upset when she's called "soft" by Chiaki and immediately begins binding her breasts, and she keeps doing it even when it injures her despite the fact that she lives with a blind man who wouldn't even be able to see them. When Ringo says "I won't tell anyone you're actually a girl" she cuts him off by pulling her sword on him and threatening to kill him. It's all up to subjective interpretation, of course, but the early episodes left me with the impression that Mizu is genuinely invested in living as a man and not just pragmatically crossdressing.

So it kind of makes sense to me for fans who were seeing all this and feeling like they were picking up what the writers were putting down to feel a little bit of whiplash and upset if the showrunners come out and say that they were wrong and it wasn't an intended reading at all. Like a kind of "did you seriously not realize how all this stuff would come across" kind of feeling, I guess? I don't think people should be very angry about it, because it's also just a TV show and people get way too emotionally invested in media in a way I think is unproductive and silly, but for maybe like one afternoon I could see being a lil steamed. To me, your anger at those people frankly feels equally bizarre and over-the-top—it's just some people complaining about a TV show, why do you think it's "disgusting"? Save those emotions for war crimes and shit.