Hmm. I'm going to add on to this post and not make my own because I do want to engage with it, even when I disagree with some (not all) of its arguments. This is because I respect the place where OP is coming from.
One factual counterpoint I would offer is that shaming does, in fact, work as a useful deterrent. Shame is not a good motivator, so it doesn't help in inspiring people to DO things, but it is a good depressant, so it does help people avoid doing things.
Specifically related to fandom and fic writing cultures, shaming has been productively used to counter both plagiarism and racist writing. I'm aware those two things are different in scope and intention. I reference both to point out the difference in how shaming as a strategy has been mainstreamed or not.
In regards to plagiarism, it is absolutely a part of dominant white fandom culture to cheer on people who track down plagiarists, and to report them and get those fics taken down. Authors thank eagle-eyed readers who spot plagiarising stories in the wild, and the OTW built in rules against plagiarism, and therefore for reporting it, into the very first iteration of AO3.
One of the fundamental arguments against using generative LLMs or 'AI' is that it is a plagiarising machine on a scale as yet unavailable to individual plagiarists. It is a fact that every free-to-use commercially funded AI software out there has currently been trained on massive amounts of stolen data--stolen in the sense that the creators of the data have not given permission for it to be used in that way, nor have they been credited, nor have they been paid for it. (I will insert my obligatory disclaimer about piracy here because there is no stripping of authorship credit there in the way that plagiarism works.)
So when you look at fannish pushback against AI as an extension of its culture against plagiarism, it makes perfect sense, that is, it is morally coherent, for the treatment that fandom extends towards plagiarists of individual works to also be applied towards industrial scale plagiarists.
This maps on to the cultural schism you can see between the fans who support OTW's stance that AI-generated work is a valid transformative form of art welcome on AO3, and those who are offended by the OTW's mendacious 'because we cannot successfully distinguish between two things, we will state that there is no difference between two things' position.
This is part of a much larger conversation around credit, attribution, and cultural appropriation, and I respect people who have differing views on all of these. But I do want to highlight that 'passing off as your own some work that was built on an uncredited, unacknowledged foundation' is literally the subject of several international lawsuits, often led by people from Global South, marginalised identities. (It's why the Geographical Indicator label exists.) And 'shame, copy cat, shame' is an artistic position that has been made across cultures and art forms, many times by artists who are not making financial profit from their art. So I see no reason why fanfiction writers and artists cannot participate in this cultural stance along with other creative people.
The second example of shaming I brought up, about racist writing, ties in to the point the OP made about "the noncon and underage labels on ao3 are morally neutral statements". I think there was also a reference in tags to the "toxic LJ culture of call-outs".
Now, I was around before the OTW was formed, and noncon and underage labels were definitely NOT morally neutral terms back then. There were many, MANY heated arguments around labelling that happened on Live Journal (and Dreamwidth) and they were extensions of arguments that happened on mailing lists, because writers and readers alike fell across a spectrum of positions from 'you are abhorrent if you publish something on the internet without warnings' to 'you are censoring my artistic freedom by asking for content notes'.
This was ALSO the same time that racism in fanfiction was being discussed, and for a brief period of time, it was acceptable, if you were a member of an LJ/DW community for posting fic for a certain fandom or theme, to be able to say, 'hey, the fic you posted is racist'. Because it was considered ok for the community to have rules like 'don't post racist stories'.
Like I said, it was a brief period of time, and one of the many things that the OTW did to shape fandom culture was to create a place where you could publish fiction, but not participate in a cultural community. And again, this is a development that has been critiqued by many writers and readers--so it is an acceptable stance for a non-white fan to say that critiquing a piece of fannish writing is fine, actually.
Which brings me to the whole 'don't like, don't read' stance that I personally find juvenile. I believe that many fans use it in good faith as a shorthand to say 'if you didn't like something, don't comment in the author's space to tell them that'.
But as OP observes, the hierarchy of who is considered a 'real' and 'productive' fan excludes certain forms of cultural creation and consumption, and the fan critic has always been on the very periphery of permissible fan. "Don't like, Don't read/watch/listen" when applied to non-fannish art, whether it is behemoth produced commercial media or endangered folk tradition, is an absolutely bonkers statement to make. It removes one of the well-springs of new and original art, which is the critique of art that people disliked enough to talk about, that seeps into cultural influences enough to be incorporated by other artists. It erases the fact that criticism of art is in itself a creative activity.
Now, I am aware that 'you used AI' is being wielded as an accusation against writers from marginalised linguistic backgrounds, and as an in-group policing tool, and as a grudge cudgel. Several of the points that OP makes deserve reflection upon.
But the reason I am making this reblog post is because these conversations are not unique to fandom. Across writing and art communities, these debates are raging, and people from marginalised identities are speaking up from all sides of the spectrum. And I want to situate the critics of AI use in fanfiction within that larger conversation. To maintain a base position of -- it is good, and necessary, for critics of fanfiction to voice their opinions.