But you still do not see, that there is no such thing as private messages on a website. They have to have moderators to intervene.
If the system is implemented properly, they are private in the sense that they are accessible only to the communicating parties until reported and even then, only the portion in question is made available to the moderators, not the whole history of everything that user(s) wrote to everybody, unlike public ones.
That was in response to your reasoning, that those messages would be "private" and hence would not need moderation and some simple features would hand wave all the issues. At least that is what I understood from you. You invoked something like that to the explanation that such messages would not be implemented "because they would be a moderation and privacy nightmare".
The part you quoted was solely in response to the screenshot issue.
and having not observed any supporting evidence for the viability of your solutions you could cite
The viability and the lack of real-world evidence was related only to the "disabled by default", not the PMs in general, not because I think this should be the new norm, but because I was informed that moderation issues were the main stumbling block. If you think this simple solution wouldn't reduce them substantialy, you are free to ignore it.
you think you know better than the people actually running such a site.
This conversation is starting to head in the wrong direction, so I will try and be very brief. Never said such a thing, unless you think that sharing ideas constitutes as "being smarter than the ones who are making this site". In that case, why does this forum section even exist?