VPNs can be made illegal if necessary. That's already the case in some countries.
I think people generally grossly underestimate the reach of the government when it comes to the internet. Ultimately they can change the very foundation of the net if they see a compelling reason.
A cryptography cat-and-mouse game would be very, very interesting; secure channels can be used to secretly architect new channels, whereas broken channels can uncover secret methods and identify nodes in order to break more channels. (I suppose it's not much different than the Drug War or WW2; most wars revolve heavily around information.)
It would take some serious marketing effort to convince most Americans that encrypted communication must imply criminality, but sadly, it could be done.
I think people generally grossly underestimate the reach of the government when it comes to the internet. Ultimately they can change the very foundation of the net if they see a compelling reason.