Re: "nat-has-nothing-to-do-with-security"
We have all seen what happened when instead of routers with NAT; people had "modems" which directly attached the computers to the Internet - a lot of systems compromised with ease.
I think you'll find that millions of systems are compromised with ease at any one time. Protection via NAT was coincidental, much like security through obscurity, and it didn't take long for hackers to work around any "protection" afforded by NAT.