Users that expect moderation expect a certain level of housekeeping and don't care if they are exposed to it all, and I would guess a great many don't want to be bothered with it.

The important distinction here is that being shadowbanned is being excluded from the community, and is done to even more effectively keep these people away from and out of the community than just regular banning would accomplish. The community expects to see content from the rest of the community, these people aren't part of that group, regardless of whether they still have an account and can log it, so the amount of deception to the community is little to none.

The alternative to shadowbanning is not letting they people post, it's banning. The effective desired outcome in both cases is that this person no longer is allowed to be part of the community. The effective actual outcome is that regular banning often just results in people making a new account and continuing with the same behavior. The only deception of shadowbanning to the community is that you're not explicitly saying "hey, these posts we tried to stop from being made? We're letting them be made but just hiding them from view, since we don't want them here in the first place."

If I'm going to get mad about that I might as well get mad at the police or a business owner for taking down some banner that was hung illegally across other businesses that I would see on my commute if they didn't act fast enough. Would I feel deceived that people had his some random message someone decided to put up that was unwanted was removed without me being able to see it? No.

> I disagree that it’s a morally acceptable way to moderate a community or forum, though.

If every forum was like that I might agree. But groups of people have the right to choose how to police themselves and there are plenty of other communities out there that do it differently.

> People lose trust when they find they’ve been shadowbanned

Those people are being kicked out. The community, or the mods, want them to lose trust and leave in most cases. I don't worry that someone I think deserves to be in jail is disillusioned because they don't think they deserve to be in jail. Or, if I worry about it, it's not in a way that makes me think they don't deserve the punishment.

> or discover that the practice is used.

I think that's very few people.

> They rightfully understand that the discourse is being manipulated in an underhanded, opaque way.

All moderation is this, whether done by the few with extra powers or outsourced to the crowd. Moderation is censorship. Censorship isn't always bad (like most things in like, it's a matter of extremes being the problem. Too little or too much both have issues, so we generally fluctuate as a society around a sort of middle area).

You can call it underhanded and opaque all you want, but it's only that to those that have already been excised from the community. To everyone else, it's really no different than if that person was banned, except they're less likely to come back for a while.