I can see the argument for planting seeds of doubt. Because although I don't think rational arguments often persuade JWs to leave the religion, little seeds of doubt can be stored at the back of the mind, ready to be deployed whenever a JW reconsiders his membership, usually initially for personal reasons. I think many former JWs have the experience of suppressing doubts and putting them aside, only to revisit them later when leaving the religion. So it's good to have these sorts of things in the mind for when they may be useful.
I always remember an apostate sign that simply read:
Matt 8:11 - proof the Watchtower is lying to you!