Earlier quoted context omitted.
You can't sign up without one, and it being an option means people who are in danger won't do it. Also, if someone's phone is confiscated, and you're in their Signal chats and their address book, it doesn't matter if you're hiding your number on Signal. It's better to just not require such identifying information at all.
That's true for any system where you have contacts linked. Same thing happens when you have names and avatars. If you don't want to link your contacts... don't link your contacts... But this doesn't have the result that the GP claimed. The whole network doesn't unravel because in big groups like these one number doesn't have all the other contacts in their system. For people that need it: | Settings |- Chat | |- Shar…
If we go full tinfoil, then do you really trust Apple and Google to keep your Signal keys on your device safe from the US government?
It's probably not that bad, but I do know that we're having some serious discussions on Signal here in Europe because it's not necessarily the secure platform we used to think it was. Then again, our main issue is probably that we don't have a secure phone platform with a way to securely certify applications (speaking from a national safety, not personal privacy point of view).