I don’t really know anything about the situation you cited.

For any community hosted by a corporation like reddit, the answer has to be pretty much: no discussion of self harm in the first person will be tolerated.

For communities hosted in the fediverse it’s more complex. If I were an admin, I wouldn’t allow a community to discuss self harm in the first person on my instance for a variety of reasons but most of them boil down to: Mods just don’t have the skills, experience, and resources to discern between what is an appropriate or inappropriate discussion or comment.

While a safe place for this type of discussion could potentially be therapeutic in some way, the potential for harm is just too high.