I think what you say about the 'echo chamber' bias is right, and I enjoyed reading it because this is something I've been pondering for a while* . It's an interesting case of a point so subtle that nearly everyone not only misses it but is sure that the opposite is true.
To answer your other concerns: Yes, we go out of our way to try to make moderation decisions individually. I don't think it would work to publish information about users' past accounts—that would be a surefire shitstorm. As you and others already figured out, 12313089 was flagged by users—that's what [flagged] always means, both on comments and stories. Vouches were turned off on direct replies, but I was inspired by the below to enable them.
To answer your other concerns: Yes, we go out of our way to try to make moderation decisions individually. I don't think it would work to publish information about users' past accounts—that would be a surefire shitstorm. As you and others already figured out, 12313089 was flagged by users—that's what [flagged] always means, both on comments and stories. Vouches were turned off on direct replies, but I was inspired by the below to enable them.
* e.g. the subthread starting at https://news.ycombinator.com/item?id=12003178, plus https://news.ycombinator.com/item?id=12003205