Earlier quoted context omitted.
> But: why bother? Email is just one of dozens of messaging systems available to Internet users. No, it's not. It's the only widely available, decentralized system, with which you can send to anyone, if you know the address. None of the big ones is this open. XMPP tried to address this and failed; now Matrix is trying again.
WhatsApp has over a billion users. There are big places where its market share exceeds that of SMS --- another big centralized service that has a userbase comparable to that of email. My conclusion is that the people who care about "decentralized" systems are a rounding error. I care about non-technologists managing to send asynchronous messages to each other that are well-encrypted by default. That's a solved proble…
What would happen if e-mail didn't exist, and a site like HN listed their WhatsApp contact information instead of an e-mail address? Suddenly, the Brazilian user base here would be unable to contact HN. They might be completely out of luck, or if the user base was large enough, HN could add an alternative contact method for users in restricted regions. "Contact us on WhatsApp. If you're in Brazil, you'll need to contact us on ABC messenger instead. If you're in China, and unable to access both, you'll need to send us a message on XYZ messenger."