Trevor, you have definitely given a good analogy. Sometimes, too, the protection mechanism seems more like one of those metal shades that small businesses use to deter thieves when the business is closed.
Initially, the shade is up and the JW appears to be open and eager to discuss issues. If arguments are presented for which they have no pat answer, the shade begins to come down. Eventually, the "Closed" sign comes out, and they shut off altogether.
The black and white thinking is extremely rigid. If the Society says that something works in a certain way, then THAT'S the way it is. If actual experience shows that the thing is NOT working the way the Society said, then the experience itself MUST be invalid and a lie, because the Society said that THIS is the way it works.
On several discussion boards, I've brought out points that JWs couldn't satisfactorily answer. In every case, the JW just disappears rather than take the chance that they might have to adjust their perception of a matter.