Avery At least you didn't try the relaxed attitude about nudity gambit.
Really only because you specifically dismissed it beforehand. When I lived with my parents, we had an unlocked bathroom door policy unless guests were over, and if one person needed to dry their hair while another was taking a shower, and I only ever minded in my teens because of the random boners I was getting. Sometimes we would even call another family member for an errand, like fetching a towel we forgot or soap that ran out. Or, and that actually happened last time I spent a night at my parents' house (without the cage, would be too embarassed to be seen in that), a plunger because the drain was too slow.
And no, I do not buy the whole "girls need modesty, boys do not" Victorian attitude that led to things like girls getting swimsuits while boys swam nude, in some cases even with a mixed-gender audience.
And again, yes, the keyholder is obviously not just randomly in the room while the wearer has their belt off in the shower. They are there to supervise, but that task can also be accomplished with open ears and maybe an occasional glance. No need to stand in front of the person and watch their every move, that would get supremely boring rather quickly.
And I am going to assume nudity privacy went out of the window for truly involuntary wearers (i.e. not people like Jen who are reluctant, but can be enticed to try it somewhat consensually) the moment the belt came into the picture. I think it is reasonable to assume that at least initial beltings would have been performed under the watchful eye of the keyholder, looking far more closely at the wearer than they ever would during a supervised shower. If they did not do the belting with their own hands, even.
Yes, involuntary belt use is abuse, and supervised showers are a part of that. We just disagree on how big a part, with me arguing that compared to the whole "interfering in sexual autonomy" and "literally locking restraints onto the body with chains and keyholes and all that stuff", a few minutes naked with another person in the room are an incredibly minor thing.
And no, my talk about how a supervised shower might look like is not mere conjecture. It was at first, a fairly bold extrapolation from my own, very unrelated, experiences, but I think it was Angelina who confirmed that with her own experience.