If the country of your choice doesn't permit you to emigrate, that doesn't mean that you're suddenly free from your obligations to whatever country will host you.
Wouldn't that be convenient? "Sir, I don't have to pay taxes. I want to move to Switzerland, but they're full right now, so I can't."
(And the "threat of prison" is some of the dumbest hyperbole out of the antitax crowd--for nearly all cases, they'll simply garnish your wages, or something equally non-freedom-constraining.)