It turns out you can put whatever text you want in the alt text field and it won't get clocked by the scolds because they don't actually care enough to check. It's enough that it appears compliant in a surface-level audit.
However, there is an issue suggesting adding an automated scold in the Mastodon client (and Megalodon already has such a scold, plus a (!) of shame on images without alt text) https://github.com/mastodon/mastodon/issues/13894
I have yet to find an actual vision-impaired person complaining about missing alt text. I'm sure there is one somewhere, but it mostly seems to be a phenomenon on Mastodon for a few people to use as a cudgel to feel superior.
I don't have impaired vision, but I use alt-text to save bandwidth on metered internet connections. For instance, if there's alt-text that says "stock image of happy traveller", well, I can probably do without that until I get a better internet connection, whereas if it's "bus timetable for this stop", it might be worth me turning on images to see that despite the cost.
I saw the comment you're talking about, but I'm not sure I understand what it meant. What does a screen reader do other than skipping an image without alt text?
Either way, that person was also explicitly saying that they don't want mandatory alt-text, that they believe an option users can toggle on their own account to be reminded about alt-text is better, so I don't think they would qualify as "complaining about missing alt-text".
It seems they don't want it to be mandatory because people will likely fill it with nonsense, as your already suggesting, which is worse for them than it not being there.
I don't know what the screen reader does, presumably tells them there is an image there. I assume they want the option to remove the post all together.
I'm not running a study, I'm making an anecdotal statement.
That said, my actual position is that inconveniencing every single person who posts an image on a microblogging service by forcing them to write a description of it on the off-chance that a tiny percentage of the population who are visually impaired will want to read it is a net evil. It will, in the short term, antagonize people who just want to post something quickly and get on with life, and in the long term drive lower engagement on the platform as it raises the amount of effort required. It's a waste of potentially a massive amount of tiny slices of a nonrenewable resource: human life time.
What should happen, instead, is that the tech wizards developing the microblogging software use computer vision and language models to provide on-demand transcription of any arbitrary image. If anyone should understand that, it's the audience here.
However, there is an issue suggesting adding an automated scold in the Mastodon client (and Megalodon already has such a scold, plus a (!) of shame on images without alt text) https://github.com/mastodon/mastodon/issues/13894
I have yet to find an actual vision-impaired person complaining about missing alt text. I'm sure there is one somewhere, but it mostly seems to be a phenomenon on Mastodon for a few people to use as a cudgel to feel superior.