Who uses ethernet?! :-)
Everyone here at UC Berkeley.
I think it's safe to say our FidoNet doesn't have three feet of thinwire in it. We're all dialup. Message-reader integrated security is where it's at -- here.
In the case of FidoNet, it sounds like that's what's needed, because your mail is being sent from systems that are not multiuser systems. The net really is just for exchanging files and mail; it isn't for remote computer access.
You're totally right about it though... but it requires physical access.
Physical access is much easier than people think. I can walk into almost any computer room here at UC Berkeley and plug in. And we have something called building ether in the building I work in: all of the machines in this section of the building are on the same ether net. This means that if we want to see other researchers' data before it's published, we can, because we can see all of their packets. e