It's interesting to note that choosing not to worry about those things ("privacy, authentication, authenticity") were very much design choices - perhaps the most consequential design choices ever?
See also SMTP which has flooded the Internet with huge amounts of garbage traffic but which is simple and works well enough that any alternatives fail.
I agree with your main point, but I wanted to add that there are plenty of alternatives to sending e-mails using SMTP these days. They mostly go by names like "Facebook" or "Google+" and run over protocols like HTTPS talking to a centralised service provider, and they solve the fundamental problem -- letting people send text and picture messages to friends/colleagues for viewing at their own convenience -- in a different and mostly incompatible way.
If business switched to facebook as the primary method of communication then facebook becomes critical infrastructure for the economy.
If it suffers downtime then there becomes a massive economic cost, so "move fast and break things" is no longer a reasonable motto.
Such a common tool needs to be highly resilient to catastrophic failure in the same way email is. For example the DDOS on sendgrid affected sendgrid and their customers but the rest of us were unaffected.
The implications of a system that allowed groups like Anonymous to cripple worldwide trade at will via DDOS would be quite scary.