I've just read the OP and all comments...Cofty's OP is spot on to try and reason with a still-in dub on their own terms...
This method may work but only as many have mentioned that the dub has a measure of doubt that they have "the truth".
What others have alluded to is the question whether this subject will actually speed up or start the "awake" process that we all have gone through.
And there is no right answer to that, some may...some may not...but the point is Cofty's OP cannot hurt because even if the dub defends the WT on this subject and refutes in his mind the argument it WILL be a building block for another doubt and when added up will help the person wake up.
This was my journey, not really one thing that woke me up but continual reading on sites like these that, when added up, I knew it was not "the truth".
Thus whilst Cofty's reasoning may not start the awake process with someone it will be a building block to it if they continue to research or query things...