Not to add flames but.... ;)

In your file access argument you claim the hacker couldn't access your files. That isn't deducible from your argument. Say for instance he got a trojan on your system, even when disconnected from the network the virus monitors. Once you then reconnect, off your precious files go over the network. Does this mean you can't make a secure system? Of coures not. Does it mean you can make a secure system?...nope. I would venture to think that computer security is like personal security. How secure you are depends on how many freedoms you want to give up. So you way trade offs, is it worth the trouble of carrying a key to have a lock on your house. What about giving up your freedom to fly without ID? Hopefully people remember this before the current security crazy gets too out of hand. Anyone its the same with computers. Are you willing to give up your internet for security? Are you willing to give up your favorite OS for a better OS that is more secure. Are you willing to enter a password to access any file to secure it? Do you use a more secure but less friendly browser? Do you set windows to always ask some stupid questions to catch those one or two spyware programs it will stop? Do you deal with firewalls? Virus scan? Adware scan? etc. The list is obviously quite large but the point is that you can probably be 100% secure...but then are you still 100% functional? Obviously the answer varies from machine to machine, user to user, circumstance to circumstanc. Just my ramblings!

"The only time a hacker has an opportunity to cause mischief is when the implementor in charge of security screws up; and he can only exploit that mistake to the extent of the screw up. Hackers can't work magic out of thin air, and in absence of mistakes to exploit, they can't do anything."

Could such a system exist? Probably. Does it? I would venture to bet not.