...huh. FBM appears to be a centralized two-way textual communcation system with a strong identity system: It's essentially the anti-IRC. What do you use for multi-way textual communication, or textual communication with weak identity (these often go hand-in-hand)? Or do you just not use either?

I should mention here that I work for Facebook. (Though I would also like to make clear that this post and anything else I do on HN is my personal opinion and does not represent Facebook in any way)

You are mistaken: FBM supports multi-way communication. For work, I use Messenger almost exclusively. For personal stuff, some combination of Messenger, Google Chat, and SMS/MMS. I do log on to IRC once in a while, mainly Freenode, but it's far from "primary".

Why does the "average" person ever need weak identity communication? I mean, I'm glad it exists and it has a niche, but why would you expect that to be someone's main way of interacting with people?

shrugs I don't know. It happens.

Anyways, there is an issue with FBM's multi-way: It's designed as an invite only system: you have a list of people you want to talk to multi-way, and you talk to them. This is fine in certain contexts, but in other contexts, the "room" abstraction used by IRC is more effective, as it allows you to have conversations with a strictly defined topic, but not strictly defined participants, the opposite of FBM. FBM's system is fine for small-scale multi-way communication between known parties, but that's not what people use IRC for.