> No, it's not. By requiring a phone number, Signal does not defend privacy. This is a binary question, there's not a grey area here. It doesn't matter that they're building a social network, or anything else. What matters is that it's not private so long as they require a phone number.

I'm not so sure. A lot of the objections to Signal using phone numbers seem similar to objecting to SSL/TLS because it's not Tor.