The problem is how broad the supposed rule is and the fact that the removals were done stealthy. If this thread hadn’t blown up after a staff member called users “pedos” for reading loli content, most people wouldn’t even have known about it.
Mangadex is a scanlation hub, so taking such a questionable approach while enforcing a rule broad enough to cover some of its most popular manga, like Kaguya-sama, Horimiya, Berserk, and many others, makes the situation worse. Applying the rule selectively, based on whether a title is “too popular to remove” despite technically falling under it, only undermines the credibility of both the policy and its enforcement which makes this entire argument more convoluted and stupid, even more if you take into account that this site is based on illegal copyrighted content which would go at it again to why they are making such attempt to be "legal" while hosting illegal content themselves.
The legal argument is also debatable. As far as we users were aware, and according to the site’s own Terms of Service, the platform operates under U.S. law, to which there is no clear legal basis against loli content and the removing of said content could even raise First Amendment concerns. We also have to take into account that If the site shifted its headquarters to the UK amid the current climate there, it’s understandable why some would see that as a deliberate move that would lead to these changes and make even less sense why they would make the move in the first place without communicating anything or changing their TOS. From that perspective, it can come across as an intentional decision by internal staff that ultimately makes the site worse in the eyes of everyone involved.
Again, even if you dislike Loli content this opens the breach to either a move to be a "legal" manga site, as Crunchyroll and Fakku did and how Mangadex has been trying to do for many years now, and the removal of many more content and cersorship of the entire site, maybe for new users, new manga readers or even younger people this seems like a blow out of proportion issue but for anyone that has been in this for many times over the years is clear as day what is happening and what they are leading on.