You mean the EU candidate countries?So what? There are other places in Europe which are in neither. Why couldn't the U.K. be the same?Iceland, Norway, Lichtenstein and Switzerland are not in EU, but they are in Schengen Zone.
Your preconceived prejudicial perceptionThat might well be so, since obviously the EU is about expansion of territory and power.How many more times? EU would insist on the Schengen Agreement in the event of a Brexit to reduce the possibility of contagion!
But you're the only one with that argument.So as I said before, the U.K. should just say "No." If that means having to accept the EU's general external tariffs, so be it.