Oh policing like that won't work
it is every man, LAN and host for themselves.
That's the only design that works, if you try and add other levels, those levels will get compromised and when they do it will be even worse.
Security is a process, that requires constant monitoring and adapting.
But to put things in perspective most traffic in the CyberSpace is legit and it is not like MeatSpace is not vulnerable to similar problems.
Take your toll house idea - break the toll house and that is a very large DDoS or a very big abuse of trust. Anarchy works it always has done, but it is survival of the fitest.
It is not so much allowing people to forge sender addresses, but more this is actually how the Net works it is connectionless, and that is its strength. The dynamic routing is another strength, this thing is designed to withstand war and still be operational albeit in a limited way.
You are not meant to blindly trust - SSL and perhaps beyond will have to be bought in as standard, and the problem there is the free browsers, that is where they make their cash, ironic really as the Net could be lot more secure if it weren't for the browser wars.
The Net will get tiered, and is already to a degree, but each tier introduces new vulnerabilities, so there will always be ways to disrupt, if people can be traced then that is about as much as you can hope for. It still ties up the attacker's machine a bit running an attack, and there is a risk associated so business as usual.