Comment by mmooss

Imagine setting up a chat for an organization you're working with - will you be willing to process 20 out-of-band QR codes? 50?

On a smaller scale, it's clear that Signal believes a functioning address book is necessary for end user adoption. For example, by default Signal notifies you of people in your phone contacts who are on or who later join Signal.

> Presumably the Signal folks can come up with more alternative solutions

I have yet to see a solution better than the one they chose, for their requirements. Notice that there are none in this discussion.