Email is a working example of federated network, and it’s profoundly different from Facebook. And not any more abusive than Twitter.
It didn't get decent until it people started flocking toward centralized solutions like GMail, which (coincidentally or not) did a pretty decent job of reining in spam and viruses.
There are many many ways to achieve the same or better results for spam protection they by using google
That's not been my experience at all. I've been running my own email server for years and I've yet to hear about an email being blocked. I know many other people who run their own email server just fine.
I think people have just become defeatist.